refs #82. Added methods and tests for navigating the history of the game.
fixed some typos
[refs #82] Added missing docstrings.
ref #82 - added a backward and forward button to the gui layout
Merge remote-tracking branch 'remotes/origin/master' into #82_history_navigation

Conflicts:
	Go_Backend_Unittest/backend_test.cpp
	Go_GUI/GUI.cpp
	Go_GUI/GUI.hpp
[ref #82] Implemented history navigation in the controller
refs #82 - changed font of buttons to the new font, added signals if button is pressed
closes #82 - defined signals, incommented the outcommented stuff
[ref #82] disable navigation button if there is no history in that direction
Merge remote-tracking branch 'remotes/origin/master' into #82_history_navigation

Conflicts:
	Go_Controller/BackendWorker.cpp
	Go_Controller/BackendWorker.hpp
	Go_Controller/main.cpp
	Go_GUI/GUI.hpp
Merge pull request #141 from augmented-go/#82_history_navigation

#82 history navigation