Fix a number of compilation errors with generic (not done yet)
Merge branch 'key-family' into key-family-instances

Conflicts:
	persistent-template/Database/Persist/TH.hs
add needed extensions for instance generation
add PersistField instance constraint
Fixes for JSON instances
fix mpsGeneric JSON instances
constrain more operations to MongoBackend
fake JSON instances for ReverseFieldOrder
Fix two ambiguity issues
Fix two more ambiguity issues
Fix a stupid bug