UInt256 Token Support

[mrtpain]

• When creating a new token, provide the option for the new StandardToken256 contract or default to it.
• Token balances and transfers should look to the contract to see if its UInt64 or UInt256 based to build transfers and approvals accordingly for the 2 different token types.

[mrtpain]

PR created #71
Dependent on stratisproject/CirrusSmartContracts#32