Feature request: Set center of rotation

[CLiersch]

This is a feature request:

Currently (TiGL V3.2.3), when rotating a model in the TiGL Viewer, the viewer selects the center of rotation automatically. However, if you want to inspect a geometry from a certain perspective, it would be very useful if you could select the center of rotation explicitly.

The classical way would be to provide a keyboard or mouse-click function to set the center according to the current mouse pointer location, projected onto the geometry.