Remove UsingRegistry patter

[martinvol]

Expected Behavior

Contracts should not change bytecode when a new contract is added to the reigstry. UsingRegistry or UsingRegistryV2 should be moved to mixins or it's own contract (not abstract).

Current Behavior

Many contracts currently inherit UsingRegistry or UsingRegistryV2 as a helper. When a new function or contract is created in these contracts, all children contract's bytecode change, and then get scheduled for releasing. This leads to confusion and big, unnecessary governance proposals.