Breakup the registry package into separate packages.

Currently all registry implementations live in a single package,
which makes it bit harder to maintain. The different registry
implementations do not follow the same coding style and naming
conventions, which makes the code harder to read.

Breakup the registry package into smaller packages based on
the registry implementation. Refactor the registry packages
to follow a similar coding style and naming convention.

This patch does not introduce any changes in behavior.
It might be the appropriate time to name this package replicationcontroller - the controller term is overloaded and we may want to prevent it from becoming worse.  `controller` more accurately describes the agents that monitor the resources of the system for consistency, and the `ReplicationController` is a type of user defined agent.