3D View navigation and zoom improvements

[JacobStoren]

See #1193 and #330

After some discussions we think the problems can be summarized as follows:

• The users are not aware of the implicit point of interest
• It is too easy to pan the rotation center out of the frustum
• When looking at sparse geometry (eg wells only) the users "never" hits geometry when initiating rotation, unless they are aware of the point of interest concept.
• It is difficult to hit tiny geometry when navigating
• Point of interest is not set when zooming or panning, which makes them behave strangely when the POI is "wrong"

Possible remedies. Needs testing and evaluation if implemented:

• [ ] Make sure POI is never outside the view frustum
• [ ] Also clamp it to be inside the BBox of the geometry inside the View frustum
• [ ] Set POI at the start of Pan-drag
• [ ] Set POI when wheel-zooming also. Use first wheel step in group of wheel actions (reset timer at wheel step. If time since last wheel step is higher than threshold, set POI again)
• [ ] Make it easier to hit sparse geometry like wells etc.
• [ ] When trying to set POI when mouse is not hitting any geometry do:
  • [ ] If zooming, set POI to ray-intersection with backface of BBox of visible geometry inside viewfrustum
  • [ ] If panning, set POI to midpoint of BBox of visible geometry inside viewfrustum
  • [ ] If Rotating do nothing (but clamping the POI)