Various fixes for migration and test cases

Migration:
- Deprecated the node "UV Domain" after confirming with Ian
- Migrated the node "Flatten Completely" to the built-in function "Flatten"
- Fixed broken and lost migration functions ("Model Curve", "List Maximum", "List Minimum")
- Updated the migration of "Selection" nodes to conserve XML subnodes which store information on the selected Revit element

Test cases:
- Made small adjustments to test cases in "Dynamo.Test.ListTests" to be able to pass
- Added test cases to "Dynamo.Tests.NodeMigrationTests" to test migrating non-core nodes including Revit, Python, Excel nodes (MAGN-2132)