No empty CBN
Empty code block node deletion with undo
Fix spelling error (NodeModel.IsConvertiable -> NodeModel.IsConvertible)
Setting of preview variable
Merge pull request #795 from ke-yu/ChocoButter

Fix spelling error (NodeModel.IsConvertiable -> NodeModel.IsConvertible)
Merge pull request #796 from junmendoza/ChocoButter

CBN syntax error crash fix.
Generate short variable names for nodes to code
Merge pull request #797 from ke-yu/ChocoButter

Generate short variable names for nodes to code
Adding test cases generated from defects.
Merge pull request #798 from riteshchandawar/ChocoButter

Added test cases generated from defects.
Merge pull request #801 from ambarish-prakash/CBNUndo

CBN changes