Updated boardModel.qml with a model created in JS

This makes it easier to test various sizes of the model with qmlscene.
Updated MineSweeper example with board and square
Created GridOfSquares to test with.
Refactored Board so it is easier to understand

Renamed private member board_ to grid_.
Added getSquare member function.
Added BoardModel subclass to QAbstractTableModel

More or less a complete example now.
Minimal example more or less complete
Removed lib/grid C++ template
Cleanup of code, fixed dummyModel "boardModel"

Fixed the dummyModel so it should be possible to run qmlscene properly now.
Merge branch 'feature/add-board-and-square' into development