Blender Git Loki

Generator panel improvements, fix memory leak

Merge branch 'master' into fcurve-modifier-panels

Add frame range panel to cycles modifier

UI: Drag and Drop FModifiers, Layout Updates

There are still problems
- Context doesn't work in NLA editor
- Lots of memory leaks for anim context.
Should find a different method for getting the context that doesn't require a "free" every time.

This also adds support for regions with panel categories to the list panel system, which was a simple oversight.

Differential Revision: https://developer.blender.org/D7997

List panel system: Support regions with categories