Blender Git Loki

CTX_DATA_BEGIN for active object only (..._from_active_object)

For now only `selected_pose_bones_from_active_object`, more options can
be added on demand.

Discussed this with Campbell Barton. We may need this only for selected
pose bones, time will tell.

GP: Fix problem with Onion Skin after last commit

GP: Redesign drawing cache to support particles

Full redesign of the cache system used for drawing strokes and handle derived frame data.

Before, the cache was saved in bGPdata and a hash was used to manage several objects with the same datablock.

Old design made the use of particles very inefficient and prone to bugs and segment faults, and especially when this was mixed with onion skinning and multiple objects using same datablock. Also, there were some conflicts with the depsgrah logic (the old design was done before despgraph was in place) that made the use of hash not working.

The new design saves the data in the object runtime struct and avoid the use of any hash to find the right data. This improves the speed and reduce a lot the complexity of the code, memory allocation, hash overload and adds full support for particles and reused datablocks.

The particles can reuse the modifiers and shader effects of the original grease pencil object.

Versioning: name screens by their workspaces

Avoids all screens in the startup file being named 'Default.###'.

Image Space: make 'UV Edit' a separate mode

This is needed for splitting UV into its own editor, see: T54744

Merge branch 'blender2.8' into greasepencil-object

Outliner: only drag element under mouse if it was not selected before

Reviewers: brecht

Differential Revision: https://developer.blender.org/D3811

Partial Revert: bring back some comments

RNA: add widget property access

Setting object position is propagated to the physics simulation even for dynmamic objects.

The velocity is also reset to 0, which makes sense after forcing a dynamic object position.
Known issues:
- in interactive mode, changing an object position by rna causes a simulation step
- setting any part of the object position or orientation causes the full matrix to be applied to physics => missing true rigid body API

Merge branch 'master' into blender2.8

Fix error disabling all addons

UI: correct face center button active state

Fix T57295: Edit-mesh modes got out of sync

Cleanup: compiler warnings

Fix UI message-bus automatic subscription

Fix T57294: Modifiers cage ignore face visibility

Tool System: option for transform drag action

See: T57203

Partial revert '#if 0' cleanup

Partially revert 41216d5ad4c722e2ad9f15c968af454fc7566d5e

Some of this code had comments to be left as is for readability,
or comment the code should be kept.
Other functions were only for debugging.

Edit Mesh: Decrease the depth bias on vertices