Begin removal of exceptions from savegame code
Revert changes to playcontroller
Check for bool return of load_game
fixup
Added if block for mp initialization and some comments
fixup game_launcher
Set savegame::loadgame correctly in scope
in in-game load dialog, check health and version before exit game

This is fixes a minor bug:
When loading a save from the in-game load dialog, as soon as the
user clicks "ok" to load a savefile, an exception would be thrown
which effectively quits the game, before determining the integrity
and version info of that file.

It's better not to exit a running game if the new game can't be
loaded, so in this commit check these things and abort before
exiting if appropriate.
Refactor part of the load game code to remove load_game_canceled_exception

Instead of throwing an exception, the relevant functions will return a false bool

Conflicts:
	src/game_initialization/multiplayer_create.cpp
	src/savegame.hpp