Make actor selection a client-only action
Move the actor selection functions to ClientAction.hs
Organize ClientAction module wrt the semantics of Commands

The remaining functions are mostly callbacks from server commands.
They may be moved to a separate module at some point.
Express some remaining client commands as ClientAction, but returning CmdSer

There are still some problems with interleaving of client and server commands.
Generalize Writer over action monads to be used for Msg and Animation
Split moveOrAttack and let client do yet a bit more of running