Merge branch 'blender2.8' into workspaces

Show alternative mode button when building without USE_WORKSPACE_MODE

Gets active mode from active object, like old mode switcher.

Move version patches from blender2.8 into version-checked blocks

Need to do that because of bumped subversion. Didn't do earlier to avoid
merge conflicts.

Fix layout cycling not working

Also added comment for layout iterator.

Merge branch 'blender2.8' into workspaces

Fix Screen not being made local when appending workspace.

Need to make Screen linkable for this to work as expected, would not
expect any side-effect here - hopefully!

Minor cleanup.

Cleanup: Deduplicate macro code, comments, redundant struct definitions

Merge branch 'blender2.8' into workspaces

Refactor workspace data accessing

Following Campbell's and Bastien's suggestion to avoid the
all-or-nothing approach of using private headers.
Instead of using private headers we do some trickery to mark struct
members or whole structs as private.
This way we don't have to go overkill with accessors/mutators but keep
them where it makes sense.

For now this adds a macro based on DNA_DEPRECATED, just to mark certain
struct members as workspace-private (throws 'deprecated' warning if used
outside of workspace.c -- this doesn't work on MSVC though, not sure on
Clang).

Also, this adds a macro to mark struct members as workspace and file
read/write private, not sure if this is really worth it. Just thought it
might be worth considering, since some data is really workspace internal
but needs to be exposed for file read/write.

Remove linkable vs appendable distinction in data-blocks.

This is complicating the code for a specific exception, which shall
hopefully be removed later even!

So better to go with a rather small, non-intrusive hack to prevent
linking Workspaces for now, link/append code in Blender is complicated
enough as it is.

Merge branch 'blender2.8' into workspaces

Transform orientations: Make code match blender2.8 as much as possible

Basically reverts e3c12bb139250b7573b and parts of cbaaeb8d9b6c95.
Decided to keep things close to blender2.8 here, D2687 can apply the
needed changes separately then.
It's okay if removing custom transform orientations behave a bit glitchy
with workspaces, all issues should get fixed with D2687.

Merge branch 'blender2.8' into workspaces

Correct error in version patch

Merge branch 'blender2.8' into workspaces

Conflicts:
source/blender/windowmanager/intern/wm_event_system.c

Fix typo in comment

Avoid unnecessary accessors by casting to generic types

Fix missing ID handling on lib-linking

Remove incorrext XXX mark