Use shift modifier to pan, use alt to zoom

Conflicts:
	src/DynamoCore/UI/Views/DynamoView.xaml

(cherry-pick)
Changed keybindings for zoom & pan, to ctrl-+ and ctrl-- (matching DesignScript and Adobe CS) and ctrl-alt-dir respectively, added menu items so these are documented and discoverable

Conflicts:
	src/DynamoCore/UI/Views/DynamoView.xaml

(cherry-pick)
Added Zoom in and out GUI control at the top right corner.
- Limit Zoom within 10% to 400%
- Zoom in and out with button, will zoom in center of viewport
Fixed Zoom using mouse and pan issue

Zoom in using mouse will change the position of the Workspace but was not updated.
Therefore it will skip the position.
Restructure zoom code to MVVM model using eventhandler
Implemented Fit to view function and added UI at top right

Added Shortcut:
   Ctrl + 0 : Zoom and fit all node in the view
   Ctrl + 0 again : Toggle between Auto Zoom Fit view and 100% Zoom
Merge pull request #477 from l2obin/ZoomPanControlBranch

Added Zoom and Fit to view UI at top right
Initiation changes for library items preview implementation
Implement Preview for Library Items (single pop-up window style)

In the next commit, multiple pop-up window can open at the same time.
Remove Tooltip feature
Completed Preview popup for Library Items (1 popup style)