Blender Git Loki

UI: Hide & shrink scroll-bars based on cursor position

Scroll-bars are now hidden unless the cursor approaches them, in which case they
smoothly grow and become more & more visible. Note that since 0d309144020168e55,
scroll-bars are drawn on top of editor contents. There's no more jumping of
buttons when scroll-bars appear.

Technical notes:
* AZones are used to adjust scrollbars based on mouse movements

We may want to support screen level AZones if we want scrollbars to also
smoothly appear when approaching them from a different area.
I also plan to make further changes to AZones to clean up stuff a bit.
* Had to move AZone handling to a post ARegion init stage, since we need the
updated View2D data from there.
* View2D masks and scroller rectangles are now updated on every redraw. It's
cheap to do that though.

UI: Draw scroll-bars overlapping with editor content

Scroll-bars used to draw in a little extra space in the editor, causing
buttons to jump a bit when they appeared/disappeared. Now they draw on
top of the buttons, just small enough to avoid bigger overlaps. Followup commits
will do further adjustments.

With this we can get rid of a hack that was calling the (often Python
defined) panel definition - the panel 'draw' callback - twice.

improved data save/load setup and added cancel bake operator

Multi-object edge collapse

Merge branch 'master' into blender2.8

Fix T54966: mathutils.noise.voronoi Memory leak

C code was not correctly handling release of temp data, not technically
a memory leak, but indeed rather annoying bug! ;)

Fix changed signature of applyModifier callback.

Merge branch 'blender2.8' into hair_guides

Merge branch 'blender2.8' into greasepencil-object

Transform: snap_object: Make snapDerivedMesh use bvhtrees from loose edges and bvhtrees from loose verts.

Bvhtrees take up a lot of memory space, reusing the common bvhtree of looptris to snap to vertices and edges is a good way to save memory.
Unfortunately we have a worse performance: worsening around 63% in the snap operation and 46% in the creation of bvhtrees.
But since the CPU time of snapping operations (no matter how higth poly the object is) corresponds to less than 0.01% of all CPU time of a blender frame, that change is not really significant.

Snapping operations on a mesh in edit mode have not changed significantly.

BKE: bvhutils: bvhkdop functions were not made to work with zero-leaf trees.

Another solution would be to modify BLI_kdopbvh.
But let's just avoid creating bvhtrees with zero leaf for now.

BKE: bvhutils: Adds support for bvhtrees from loose edges.

BKE: bvhutils: Adds support for bvhtrees from loose verts.

Armature: Add back relationship lines.

Object Mode: Use stipple shader for relationship lines.

Reset number values when entering an empty value

Note: This rely on the property having a pre-defined default.

Also, be aware that trying to multi-drag and multi-ui-edit is not working
at the moment (T54976).

With changes by Campbell Barton.

Differential Revision: https://developer.blender.org/D3207

RNA default: Scene start/end frames

Fix wrong header alignment in user preferences, after recent commit.

UI: fix popover menus sometimes going off screen, after recent commit.

UI: keep header top/bottom alignment the same when switching editor types.