Migration overhaul

Removed the migrations from the root socialregistration app and added migrations to the individual apps.
For the files that already existed, I did merely move them. The reason being that the `0001` migrations are already in our DB and if we were to make a change to them, they wouldn't actually run on our DB, hence deviating the state of our DB from the one defined by the latest migration. 

I added migrations for the other contrib folders in the socialregistration app that we didn't have replacement migrations for completeness. (They aren't going to run on our servers because they aren't in our `INSTALLED_APPS`.)