Make toggle to canvas from 3D background preview returns focus to search view.

MAGN-498 After switching between background preview and canvas, caret not visible.
Merge pull request #877 from l2obin/MAGN-498

MAGN-498 After switching between background preview and canvas, caret not visible.
Move Zoom value to Configurations
Panning in PanMode also update WorkspaceModel's offset without triggering its PropertyChanged
1. Updated "NodeModel.ValidateConnections" to not remove "ElementState.ERROR"
2. Introduced "NodeModel.ClearError" method to compliment "NodeModel.Error" method
3. Updated "NodeModel.State" property setter to not raise change event if reporting is off
4. Updated various codes that call "Error" method to also call "ClearError" for success case
5. Updated "Formula.FormulaString" property setter to raise "State" change event
Remove mouse area, it was not needed due to EndlessGrid
Adding removal of registration of event handlers during DataContextChanged to
prevent binding multiple event handlers on the same datacontext causing one
operation to run multiple times on dynWorkspaceView.
Added unit test case "ValidateConnectionsDoesNotClearError" for defect verification
Merge pull request #882 from l2obin/MAGN-741

MAGN-741 Fixed Zoom level is too fast after fit view or switching workspace
Merge pull request #887 from Benglin/StatesAndReporting

Fix MAGN-919 Errors disappear if user clicks on the node