Refactor Selections plugin

Since the Visual editor supports Selections fields some refactoring has been done to the Selections plugin. This had to be done in a backwards compatible way. With this new major release more refactorings can be done:

• the package names of classes that moved from the cms module to the repository module can be updated
• the default implementation of methods in interfaces must be removed (implementations must now implement the methods)
• deprecated methods must be removed