Blender Git Loki

Merge branch 'master' into GPencil_Editing_Stage3

Initial stub callbacks for grab brush

GPencil Sculpt: Tweaked how strength values are interpreted for thickness brushes to be more controllable

GPencil Sculpt: Improve header infotip

GPencil Sculpt: Draw a '+' cursor when in sculptmode

GPencil: Minimum-working-version of new Stroke Sculpting functionality

Usage:
* In Stroke Edit Mode, EKEY will start the modal brush operator, using the active
brush (set via the Toolbar)
* LMB-click-drag to sculpt, release to stop.
* RMB/ESC to stop editing
* Scrollwheel to increase/decrease brush radius
* Shift-Scrollwheel to increase/decrease strength
* Hold Ctrl to invert the brush action

Notes:
* Currently only "Thickness" brush is implemented. This adjusts the stroke thickness
as you "paint" the effect onto the stroke. (Recommended Strength: 0.093)
* Strength and radius are not correctly initialised yet (to be fixed soon)

Code cleanup - Formatting

GPencil Editing UI: Move editing toggle to the main panel

In preparation for a brush-based editing tool, moved the Stroke EditMode toggle
to the main toolshelf panel so that the editing panel can be collapsed when only
the brush panel is needed.

Also, improved the tooltip here.