Make UUIDs iterable on utility chain

[jasonklein]

Makes UUIDs iterable on utility chain:

• changes registeredTokens mapping visibility to public
• removes registeredTokenProperties in favor of auto-generated getter, registeredTokens—platform does not appear to use registeredTokenProperties
• inherits from the already-imported STPrimeConfig, strikes certain constants from OpenSTUtility in favor of those from STPrimeConfig, and attendant changes (the platform does use the auto-generated constant getters)
• adds a public state var, uuids, that's a dynamic bytes32 array
• pushes UUIDs into the uuids array in registerBrandedToken (and in the constructor of OpenSTUtility for STPrime)
• adds function, getUuidsSize, to return size of uuids

Fixes #89

[benjaminbollen]

LGTM