Add the computing progress bar.
Make X.parser.reslice2 a real static function rather than calling the X.parser.prototype.reslice2 which looses the this context.
Use the new static functions in the parsers.
Propagate the first volume rendering orientation directly to avoid double calculation.
Latest test.
No errors when activating volume rendering and moving it around.

The progressbar is still not updated yet.
Clean way of showing/hiding the computing progressbar and fire the appropriate callbacks.

Unfortunately, the progressbar does not yet have time to update properly. We need to put more timeouts in the computation loop.
Merge branch 'master' into addcomputingprogress
Merge branch 'master' into addcomputingprogress
Add the X.renderer2D.onSliceNavigation callback which enables modifying sliders etc. when the 2D slice navigators are used.
Show progress during computation for volume rendering (in 25% steps).
Merge branch 'addcomputingprogress'