Bring back per-viewport localview. This is based on Blender 2.79.
We have a limit of 16 different local view viewports.
We are using both the numpad /, as well as the regular /.
Missing features:
* Hack to make sure lights are always visible.
* Make rendered mode with external engines to support this as well
(probably just need to support this in the RNA iterators).
* Support over 16 viewports by taking existing viewports out of local view.
The code can use a cleanup pass in the future to unify the test to see
if an object is visible (or we can use TESTBASE in more places).
I thought about having a single error message, or to use BKE_reportf to just
add the "s". That would be bad for translators, so now we have two
explicit messages.
Add tool options to control how select operates (add/sub/set/and/xor).
Note: edit mode armature select still needs to support all options,
this is complicated by how it handles partial end-point selection.
Before that depsgraph tagging was done from inside notifier listener in
viewport. This had the following issues:
- If there are no viewports, selection tag was not done. Causing possible
issues when object becomes visible.
- Required special trickery to detect which data to tag for update.
- Was causing crash when transforming/selecting markers in clip editor.
This is because selecting marker needed to poke viewport to redraw, since
selected bundles will be displayed differently in viewport.
