Make RecordableCommands be based on DynamoModel rather than DynamoViewModel
core refactoring
code refactoring
Merge pull request #2522 from marimano/master-core-split

Move RecordableCommands into DynamoModel
Merge branch 'master' of https://github.com/DynamoDS/Dynamo into Revit2015
Merge pull request #2558 from Benglin/Revit2015

Merge branch 'master' into 'Revit2015'