Fixed small compilation warnings.
Added saving support for selection objects.

Only saving is currently supported. Some comments were added to
note things left to do as further cleanup passes.

Some behaviors have changed:
- The root objects of the selection list are not cyan anymore.
Removed lock to crosshair mecanism.
Added loading possibility for boxes and ellipsoids.

VOIs to come.

The UI widget for selection objects is also populated.
Changed fiberIdType to use DatasetIndex instead of wxString.

This fixes issue #140.
Added saving capabilities for VOI.

If the anatomy used to generate a VOI is not currently saved, it will
show a dialog box and ask if it should be saved. If so, it will be saved
in the same directory as the scene file.

Removed the link between the anat pointer and the VOI. They
didn’t (and won’t) update automatically when the slider is moved.