[LDCad] Dropping Frame Rate when MPD View is open in Part Bin

[Roland Melkert]

My question is more towards the direction if the rendering of the preview-images can be reduced, e.g.:
- only once a part has been placed, or e.g. a second after a part has been placed.
- only after you press "end" of "Ctrl-End", i.e. render them only once.

It currently invalidates all depended renderings whenever something changes (new part,part move,color change, etc).

But I guess I could add some kind of option to disable real-time updates for part bin cells, I will look into it.