Updated ClientApplication
Updated a number of simpler client scenes (read more)

Updated the ClientApplication class to help support the new design, but
it's not finished because of that module's dependence on the various
scenes.

Updated the following scenes:

* CleanUp
* MainMenu
* OptionsMenu

The following source files (in client/scenes/) compile correctly:

* base_scene.cpp
* splash_screen.cpp
* clean_up.cpp
* main_menu.cpp
* options_menu.cpp

The folling source files (in client/scenes/) do not compile:

* in_world.cpp
* in_combat.cpp
* lobby_menu.cpp