Diagram Editor: Having multiple palettes for one Diagram is problematic

[till-f]

As an application developer I'd like to avoid problems that occur when multiple - maybe “conflicting” - palettes exist for one overall diagram (with sub-diagrams). There should be the option to have only one palette (no extra palettes for sub diagrams). It should only be in the responsibility of the palette entry whether the corresponding element can be inserted at the drag destination or not. Contributing additional palette entries should be possible using a dedicated API.