Update HTTP -> HTTPS

Re-enable solidity coverage

Use uint256 in TokenTimeLock contract

- Upgrade version
- Re-enable in travis.yml
- Move mocks to contracts folder for instrumentation

Consistent spellings of reentrant

URLs were updated to use HTTPS protocol

Changed `rentrancy_lock` variable to `reentrancy_lock`

Burnable Token should be inherited from Basic Token issue#596

feat: RBAC authentication contract and role library

There's no need to throw when burning 0 tokens

Throwing when trying to burn 0 tokens is an unnecessary special case.
If another contract wants to burn() a variable amount, it should not be forced to deal with this special case of burning 0.

Minor standards and cleanup additions.

Add docs for DelayedClaimable

feat: remove yarn in favor of npm

fix: make SplitPayment payable by default