Add todo note on sphinx
Revise client-side server abstractions

The client has no abstractions of the server-side infrastructure more
suited to allow for user code to customize it.
Modify update mechanism of client view

A client may now subscribe to models via the client view. The authorization
handling has been removed on the other hand, since it may be implemented very
differently depending on the user application.
Add examples to todo list

Tic-tac-toe and battleships serve best for a simple demonstration of
capabilities.
Revoke exposition of subscription mechanism

This might not be a good idea after all.
Move ModelLoader to model module

It simply makes more sense over there.
Add method to retrieve single update in ClientView
Remove superfluous imports