frontend: Migrate to use the new MetaMask API

[manuelwedler]

Fixes #338

MetaMask removed the injected window.web3 object recently, which we relied on. This broke our integration of MetaMask.

MetaMask should now be used through the window.ethereum API, which is specified by EIP 1193. This PR migrates the frontend to use this API to make the transaction request. The only place where we send a transaction from the frontend is for funding the user account.

This uses a small library (@metamask/detect-provider) to detect the rpc provider as recommended by MetaMask.

[codecov]

Codecov Report

Merging #339 (8359d35) into develop (ca869af) will decrease coverage by 24.95%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           develop     #339       +/-   ##
============================================
- Coverage    89.57%   64.61%   -24.96%     
============================================
  Files           22       22               
  Lines         1775     1775               
============================================
- Hits          1590     1147      -443     
- Misses         185      628      +443     

Flag	Coverage Δ
python-integration	53.07% <ø> (-30.82%)	⬇️
python-unit	40.20% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
raiden_installer/web.py	19.11% <0.00%> (-71.57%)	⬇️
raiden_installer/web_testnet.py	26.66% <0.00%> (-70.00%)	⬇️
raiden_installer/shared_handlers.py	32.27% <0.00%> (-64.15%)	⬇️
raiden_installer/transactions.py	46.93% <0.00%> (-48.98%)	⬇️
raiden_installer/utils.py	67.16% <0.00%> (-25.38%)	⬇️
raiden_installer/token_exchange.py	81.67% <0.00%> (-16.04%)	⬇️
raiden_installer/account.py	86.23% <0.00%> (-13.77%)	⬇️
raiden_installer/ethereum_rpc.py	77.89% <0.00%> (-13.69%)	⬇️
raiden_installer/network.py	77.55% <0.00%> (-8.17%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ca869af...8359d35. Read the comment docs.

[ezdac]

Looks good as far as I can tell. Added some questions, but most of them are out of curiosity.
Please ignore if the answer is obvious.
I believe the 1 missing error handling should be implemented though.

[ezdac]

Do you even need this method, and is there a scenario that this will not return an empty list?
I undertstood it that way that the eth_requestAccounts should be generally used.
This is ok for the user, since there will only be a UI-prompt when access is requested the first time (?)

try {
    // Request account access if needed
    const accounts = await ethereum.send('eth_requestAccounts');
    // Accounts now exposed, use them
    ethereum.send('eth_sendTransaction', { from: accounts[0], /* ... */ })
} catch (error) {
    // User denied account access
}

(from EIP-1102)

I could be wrong - so I'm mainly just curious.

[manuelwedler]

The user may already have given the allowance to access the accounts, when the button is clicked. For example in case the button is clicked a second time after canceling the first transaction.

In my understanding, every call to eth_requestAccounts may trigger a user interface, depending on the RPC Provider. Since this is not the case with MetaMask, I think we can just use the call to eth_requestAccounts.

[ezdac]

Ok - I couldn't find anything about eth_accounts being unlocked by the eth_requestAccounts as well,
and the example code from the metamask docs was using eth_requestAccounts just before a transaction.

[ezdac]

Looks good