- Replaced several assertions with runtime_error's to detect them in
release builds
- Removed multiple dispatchMainThread calls in server shutdown code to
simplify debugging and code flow
- Moved handling of gameplay shutdown and score calculation from
PlayerInterface to ServerHandler (not perfect, but better than before)
- added compatibility method to Canvas to allow SDL_Surface access
- added drawBorder method to Canvas to replace CSDL_Ext method
- added drawColor method to Canvas to replace CSDL_Ext method
- minor changes to Tavern and Trade windows to adapt to new API
