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.
Renamed "AsyncTask.ExecuteCore" to "HandleTaskExecutionCore"
Renamed "NodeModel.RequestVisualUpdate" to "RequestVisualUpdateAsync"
Introduced an empty "NodeModel.RequestValueUpdateAsync" method
Merge pull request #2987 from Randy-Ma/Revit2015

Merge the master branch to the Revit2015 branch
Fix for completion while typing when starting typing in middle of string
Enable mark and sweep garbage collection strategy
Disable Heap.Verify() in mark and sweep
Allow auto-insertion of highlighted autocomplete item only on certain keys
Fix for Selection Box

Fix for Selection Box
Update README.md
Merge remote-tracking branch 'origin/master' into Revit2015
Beginning of zero touch example.
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.
Build fix for method with incorrect signature
Merge pull request #3001 from Benglin/master

Build fix for method with incorrect signature
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.