TVB-2748 Remove Operation.xml files

Created by: VinczeRobert

I did the initial clean-up of code that was related to the Operation.xml files. I did some tests in the UI and it seems to not cause any problems so far.

I didn't test the creation of links for datatype, I think that functionality is not implemented, cause I don't see where in the UI could I link a datatype to another.

I pushed this now because I am curious to see how many tests fail in Jenkins.

Also, the importing of a new project (not the default one) gives "TypeError: init() missing 1 required positional argument: 'view_model'", but with these things removed it uploads the project, but not the datatypes inside, so I will try to fix that as well if we consider it related to this task.