Fix: MAGN-159 (nodes are not editable after undo/redo)

**Problem**
"NodeModel.interactionEnabled" and "state" data members are not included when a NodeModel is serialized for undo. Therefore, during a redo-operation, these states are defaulted to "false" and "dead" respectively, causing a node view to be disabled.

**Solution**
Record both "interactionEnabled" and "state" data members of NodeModel in SerializationCore method when the SaveContext is set to "SaveContext.Undo".

**Unit Test**
Passes DynamoPythonTests, DynamoCoreTests, DynamoCoreUITests and DSCoreNodesTests

No meaningful unit test cases can be written for this as this is a pure visual thing. When the command framework is put in place, then the node states can be validated after undo/redo operations. For now that is not possible.