Create a common interface for different multi widgets (editors) to allow to substitute the `QmitkStdMultiWidget(Editor)` in classes / functions that currently need a `QmitkStdMultiWidget(Editor)`, but should work with the new `QmitkCustomMultiWidget(Editor)`.
Is this reasonable, or should we strive to create a custom multi widget (editor) in a way that we can substitute the custom variant for the standard variant (and change all occurrences of std with custom)?