Two-Part Payment Support

[Zagan202]

Description

Adds two part payments (aka claimableBalances) to the deposit flow.
In the past when accounts attempt a deposit

Old Flow

1. The Wallet will initiate a deposit to an account that does not exist yet,
   or the user's account won't have a trustline to the asset's issuer account.
2. Polaris will be run periodically via the poll_pending_deposits
3. Polaris calls DepositIntegration.create_channel_account() for the transaction record (which creates a temporary, per-deposit-transaction-object Stellar account)
4. Polaris will then mark those created accounts as pending_trust
5. The Wallet will then communicate to the user that the transaction could not be completed until a trust line is established.
   for their own account or the one that was created for them
6. Polaris will call periodically check_trustlines (a command line tool that periodically checks if the
   transactions with this status now have a trustline to the relevant asset).
7. When the user establishes a trustline Polaris will submit the transaction to the stellar network and call the
   after_deposit integration function once its completed.

Desired Flow

1. The Wallet will initiate a deposit to an account that does not exist yet,
   or the user's account won't have a trustline to the asset's issuer account.
2. Polaris will be run periodically via the poll_pending_deposits
3. Polaris calls DepositIntegration.create_channel_account() for the transaction record (which creates a temporary, per-deposit-transaction-object Stellar account)
4. Polaris will then mark those created accounts as pending_trust
5. Polaris will be run periodically via the poll_pending_deposits
6. Polaris will create a stellar deposit (create_stellar_deposit) create_transaction_envelope where it will build the transaction as a claimableBalance
7. Submit the transaction and mark the status as completed.

Addresses issue: #316
resolves stellar/stellar-protocol#747

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• tests/processes/test_create_stellar_deposit.py

[JakeUrban]

Good start, at a high level everything looks good here.

The key feature I'd like to see is a Transaction.claimable_balance_id column that gets populated on successful TX submission.

Other than that, there are some small adjustments to make, and I also think we could add to the documentation to explain when Claimable Balances are used in Polaris.

[JakeUrban]

Nice, looks good pending my comments.

Also: Did you add black to your git commit hook?

[Zagan202]

Nice, looks good pending my comments.

Also: Did you add black to your git commit hook?

I did now haha

[JakeUrban]

@Zagan202 thanks, can you format the code in a commit and push? I think you just need to change whitespace and black will format the code prior to commit.

[Zagan202]

@Zagan202 thanks, can you format the code in a commit and push? I think you just need to change whitespace and black will format the code prior to commit.

Thats strange everything seemed to check out on my end
I'm getting black....................................................................Passed
Could I see what your .pre-commit-config.yaml is?

[Zagan202]

Also ran pre-commit run --all-files for good measure.
All the failing files (then formatted) are ones I didn't make changes to.
Would you want me to format and commit those?
I thought its ideal to keep this PR focused on changes that directly impact the issue,

pre-commit run --all-files                            
black....................................................................Failed
- hook id: black
- files were modified by this hook

reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/integrations/javascript.py
reformatted /Users/lawrence/stellar-dev/django-polaris/example/server/migrations/0003_auto_20200222_0003.py
reformatted /Users/lawrence/stellar-dev/django-polaris/example/server/migrations/0005_auto_20200702_1908.py
reformatted /Users/lawrence/stellar-dev/django-polaris/example/server/migrations/0006_auto_20200615_2046.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/tests/processes/test_watch_transactions.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/settings.py
reformatted /Users/lawrence/stellar-dev/django-polaris/example/server/settings.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/management/commands/watch_transactions.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/shared/endpoints.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/sep31/transactions.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/tests/shared_endpoints/test_transactions.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/tests/sep6/test_deposit.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/migrations/0001_initial.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/tests/sep12/test_customer.py
reformatted /Users/lawrence/stellar-dev/django-polaris/polaris/polaris/tests/sep31/test_send.py
All done! ✨ 🍰 ✨
15 files reformatted, 111 files left unchanged.

[JakeUrban]

All I ever do is git commit -m ""; git push

(django-polaris) ~/Documents/workspace/stellar/django-polaris (master) $ black --version
black, version 19.10b0
(django-polaris) ~/Documents/workspace/stellar/django-polaris (master) $ cat .git/hooks/pre-commit
echo "Formatting code..."
black polaris
black example
git add .

[JakeUrban]

LGTM!

[JakeUrban]

We can merge this and simply hold off on including it in a release until anchors are expected to use claimable balances.