Blender Git Loki

Camera tracking: interface cleanup and small buttons renaming

- Move tracking-related constraints to own section in list
Currently there are only two constraints, so can look a bit odd,
but it'll be other constraints like "Object Solver" and so.
- Move motion-tracking parameters from 3D viewport Display panel
to it's own panel.
- Get rid of "Bundle" in 3d viewport. It's quite obvious that it's
a 3D representation of tracks is used in 3D viewport and it shouldn't
be so confusing for artists now.
- Also get rid of "Bundle" in Follow Track constraint.
Old files can change a bit because of changes in DNA.
- Also get rid of "Bundles" in operator which creates vertices cloud
from 3D position of tracks.
- Rename "Principal Point" to "Optical Center" in the interface.