[refs #106] Only allow board sizes 9, 13 and 19, display error message otherwise. Added slot and signal for displaying error messages.
Merge branch 'master' into #106_invalid_board_size_error_message

Conflicts:
	Go_Controller/BackendWorker.cpp
[refs #106] Reverted some changes made in #80 (regarding UpdateResult) and only display error messages via the displayErrorMessage signal. The error messages are now only triggered from the controller, this makes it less complicated (I hope).
[refs #112] Added slot to gui for disabling the board selection buttons. The buttons are now disabled by default and get enabled when a newImage signal arrives.
[refs #112] The controller now sends a signal when no camera image could be retrieved. Error messages will be displayed in that case or when the scanning failed.

The debug image when no camera is connected is still enabled for now, remove the ENABLE_DEBUG_IMAGE define in Scanner.cpp if you want to test.
Merge pull request #127 from augmented-go/#112_no_camera_image

Closes #112 - no camera image