Updates BoardRules - A move to prison is no longer legal
Appends MouseEvent handlers to the ImageView of each game piece.
Pieces can now be moved by mouse dragging, although very wonky
(flickering and dead zones...)

Removes old unused ImageViews from gameboard.fxml (conflicted with
events on the new pieces).
Improves moving of pieces in GUI

Pieces can now be dragged from one spike to another.
Flickering and dead zones errors fixed.
Works in PieceController, BoardController and gameboard.fxml
Merge branch 'master' of https://github.com/eldamir/kea-backgammon-project.git
Merge branch 'dev'