Unify refactoring specific handling for CE commands

[MDoerner]

So far, we only have one refactoring command in the CE. This is why no CodeExplorerRefactoringCommandBase has been introduced so far, in analogy to the other ones for refactorings. Since we will soon have another refactoring command in the CE, we should add that base class.

Unfortunately, this will not be able th inherit from RefactoringCommandBase because it already has to inherit from CideExplorerCommandBase.

[bclothier]

One possible option is to make RefactoringCommandBase a protected backing field and delegate work to it. If the field needs to be extended, we might consider creating a nested type deriving from `RefactoringCommandBase‘ and use it for the backing field and hopefully minimize code duplication this way.