* Measure Panel - Version 0.8.7

* API change: ngon_tesselate -> ngon_tessellate
* Use persistent handler (scene_update in scene_update_post) for geometry calculation to reduce CPU load when idle.
* Remove all properties when add-on is unregistered.
* Minor: Moved text offset constants to the other script constants.
* TODO: Still heavy load while doing simple translation/scaling/rotation though. Is there a way to avoid that?