refs #82. Added methods and tests for navigating the history of the game.
fixed some typos
[refs #82] Added missing docstrings.
[ref #4] loading a game from an sgf file!
[ref #4] checking the board size of the loaded game from sgf
[ref #4] moved the board size check out of the game backend

This allows to dispatch an error message from the controller and don't discard the current game
Merge remote-tracking branch 'remotes/origin/master' into #4_loading_game_from_sgf

Conflicts:
	Go_Backend/Game.hpp
[refs #4] Add a signal/slot for popping up a messagebox for error messages

Also refactored the loading routines and fixed a memory leak if the loaded game has a missing board size or has a board size that is not supported.
[ref #155] Discard invalid stones (out of bounds) for the current board size

Reason: Not discarding them would trigger a runtime assertion which ultimately closes the application
[refs #4] Fixed bug where the controller didn't consider the game to be initialized after loading the sgf. Caused the sgf to being discarded when switching to virtual mode or when starting the scanning.
Merge pull request #158 from augmented-go/#4_loading_game_from_sgf

#4 loading game from sgf