Upgrade contracts to Solidity 0.5.5

[abandeali1]

Description

• Upgrades most contracts to Solidity 0.5.5 (except those that will not be redeployed)
• Makes the minimum necessary changes to get the contracts to compile and pass tests with the new Solidity version
• Uses new optimizer settings (saves ~3.5k gas / fill!)
• Updates ganache-cli and solcjs versions
• No longer re-export external contract dependencies within each package (this was causing incompatibility between packages)
• Note: this still compiles with evmVersion: 'byzantium'. It appears that compiling with 0.5.5 introduces some new opcodes that cause the contracts to not deploy. Updating ganache-cli did not fix the issue (even though it supports Constantinople). This should be fixed in a separate PR.

Testing instructions

Types of changes

Checklist:

• Prefix PR title with [WIP] if necessary.
• Add tests to cover changes as needed.
• Update documentation as needed.
• Add new entries to the relevant CHANGELOG.jsons.

[merklejerk]

Won't build for me because contracts/erc20/tsconfig.json still references ReentrantERC20Token.json.

[coveralls]

Coverage increased (+0.02%) to 85.167% when pulling 22af796 on feat/contracts/solidity0.5.5 into 9e03e1c on development.

[hysz]

Looks good to me!

[merklejerk]

exchange-forwarder is still at 0.4.24. Is this intentional?

[abandeali1]

@merklejerk that is intentional, but we'll make the change when the Forwarder is ready to be updated.