Alex/move erc20 wrapper and add specs

[asoong]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 492

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 229 unchanged lines in 17 files lost coverage.
• Overall coverage decreased (-97.9%) to 1.775%

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Files with Coverage Reduction	New Missed Lines	%
contracts/lib/CommonMath.sol	1	0.0%
contracts/core/extensions/CoreExchangeDispatcher.sol	2	0.0%
contracts/core/SetTokenFactory.sol	2	0.0%
contracts/core/lib/ExchangeHandler.sol	3	0.0%
contracts/core/extensions/CoreFactory.sol	4	0.0%
contracts/core/TransferProxy.sol	4	0.0%
contracts/core/extensions/CoreInternal.sol	5	0.0%
contracts/core/lib/OrderLibrary.sol	5	0.0%
contracts/core/lib/CoreState.sol	7	0.0%
contracts/core/lib/CoreSharedModifiers.sol	8	0.0%

Totals
Change from base Build 484:	-97.9%
Covered Lines:	5
Relevant Lines:	242

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💛 - Coveralls