GUI: rm SelectionDescriptor for detector alignment

Rectangular detector alignment is now handled without creating a SelectionDescriptor.

Steps of SelectionProperty/Descriptor refactoring:

1. make SelectionProperty less generic, make catalogs usage mandatory, not optional
2. reduce usage of ad hoc SelectionDescriptors, e.g. descriptors that are not derived from SelectionProperty
3. move Descriptor functionality to Property
4. use Property instead of Descriptor
5. remove Descriptor from code
6. refactor serialization of Property

This MR is related to points 2.

added GUI simplify labels

requested review from @j.wuttke

assigned to @m.svechnikov

changed the description

marked this merge request as ready

approved this merge request

merged

mentioned in commit d1632bea