Improve signatures of RedisClient/RedisDatabase.

 - Support Nullable!T as a way to determine key/field existence
 - Uses better template constraints for template type parameters/return values
 - Uses 'scope' parameters where possible
Implement RedisHash.get analogous to AA.get.
Bugfixing and improve the naming capabilities of RedisCollection.

 - Field names have been off, resulting in no correct data being written to Redis
 - Every ID for multi-ID collections can have a name, resulting in nicer nesting
 - An optional suffix can be used to "nest" collections inside of each other
 - Added RedisCollection.isMember