Clean up the implementation of the Client SDK to fit these requiements:

• Every public class, method and variable has decent JavaDoc
• Every public class is declared final
  • Specifically the classes an API consumer will use
• Every public method argument is final
• Singletons and there member variables don't store any state

Prepare a sample client implementation to show example usage of the API using our demo server.

This implementation should include:

• login/logout
• Fetch a specific office
• Fetch a client
• Fetch a staff and assign to client
• Fetch a Group and assign a client