Fix 692 - Crash Opening Graph Panel

* remove "get_window()->get_update_area()" call
Graph Panel : Fix curves line witdh
Graph Panel : Fix scrolling
Fix 693 - Graph panel, mouse wheel should just scroll ...

Now,
* MouseWheel --> Scrolling
* Ctrl+MouseWheel --> Zoom
Typo
Fix 708 - Panel contextual menu (close) is empty

item->show was missing.
Improve skeleton deformation
Z-Order field for Bone
Use bone z-order in skeleton deformation layer