Partial crossing drag-drop implementation.

Still to do:
- Move image of crossing along with cursor while dragging
- Automatically refresh the screen once crossing is added in order to display it on screen
- Give suitable error message if crossing cannot be dragged to a particular position.
Merge remote-tracking branch 'origin/ashish'
major fixes

-implemented clear grid
-fixed adding crossings (draging)
-slight changes in designer
-fixed problem when resetting crossing
selectCrossing on the screen
partial select crossing and delete crossing

showing the information on the side pane has to be done
deleting crossing needs to improve merging deletion also
design changes
merge with master
fixes in GUI
more changes...

still cant save
nothing much