Enabled C++11
Front-end now handles mouse events

Each square now handles left and right button presses and propagates the
data to the main window in QML. This makes it possible to connect the signal
to CPP slots.
Model now supports locking a square and visiting

* If left mouse button is pressed in a square and that square is not locked
and has not been visited before it will now set isVisited to true.

* If left mouse button is pressed in a square and that square is locked
nothing will happen.

* If right mouse button is pressed in a square, that square will toggle
between locked and unlocked unless the square has been visited previously,
in that case nothing will happen.