introduce layer oriented sample editor

This MR introduces the layer oriented sample editor. This MR still does not contain the integration into the GUI, which comes in the next MR.

It contains

• a lot of xxxForm classes, which represent the widgets to edit the values and structure of the sample
• comments introduced with // #baLayerEditor; they mark TODOs
• a few refactorings
• a few new methods in existing code
• a few new icons

The editor is still not 100% complete (e.g. not all Interference functions are supported, not all modifications are undoable); this will follow in future commits.