Blender Git Loki

UI: Re-arrange Shading popover

* Unify X-Ray/Shadow toggle and factor, using the whole width gives you finer control
* Shadow settings next to intensity slider
* Cavity settings next to Ridge/Valley sliders
* Collapse Cavity settings when not used
* Make MatCap preview and browser dialog smaller. MatCaps are added by the user
so she is already familiar with how they look. No need to preview them that big
while browsing. To see the MatCaps in detail we have the User Preferences/Asset Manager.

Having popovers inside popovers triggers some minor glitches that will be addressed later.
(e.g. they open on mouse over and the popover arrow is not aligned)