* Consolidted ERC20 Interface and Implementation Files
* Fixed CanReclaimToken's tests to use StandardTokenMock instead of BasicTokenMock
* Changed token's variable type in TokenTimelock to ERC20
* Merged the StandardBurnableToken with BurnableToken since it now inherits from StandardToken; Fixed TokenTimelock so it uses SafeERC20 for ERC20
* Fixed variable type for _token in TokenTimelock constructor
* Fixed linting warning in BurnableToken
* Added back burnFrom tests.
* Add StandardBurnableToken implementation
BurnableToken that extends from StandardToken and adds a
burnFrom method that decrements allowance. Equivalent to
a transferFrom plus burn in a single operation.
* Return event object from expectEvent helper
* Add comment on Approval event in burnFrom function
* Improvements on burnable token tests
- Inject initial balance as a parameter to the behaviour
- Use expectEvent helper for assertions on events
- Use chai bignumber for numbers
- Change to bdd-style assertions
