Preset operators should avoid using `bpy.context.object.data` as a base
path to properties. This path is not available in the buttons context
when using pinned datablocks! Instead use the specific
`bpy.context.camera` and `bpy.context.lamp.sky` paths now, which lead to
the correct datablocks in any case.
- Changed some names so now people who aren't really familiar with
motion tracking can understand what they exactly means
- Also cleaned up and rephraded some descriptions
- Changed behavior of operator which creates empty for 2d tracks:
now it operates on all selected tracks rather than active track only
- Added checkbox to enable/disable rotation stabilization
