Fix for selection box dragged out of canvas.

Fix for User gets stuck in selection mode when selection box is dragged
out of canvas.
Fix for Selection box dragged out of canvas

Commented the mouse leave event on WorkspaceView.
Fix for selection box dragged outside the canvas

Removed the mouse leave event on Workspace view.
Captured the mouse event on LeftButtonDown and  released the mouse
capture on LeftButtonUp. This will ensure that selection is not lost
even when the mouse is dragged outside the canvas.
Handled the mouse lost focus event on DragCanvas. This will ensure that
selection is removed if the mouse is released outside the canvas.
Fix for Selection Box

Fix for Selection Box
Merge pull request #2865 from ramramps/Selection-Box-fix

MAGN-3210 : User gets stuck in selection mode when selection box is dragged out of canvas.