Merge remote-tracking branch 'origin/blender2.8' into temp-outliner-visibility

Merge remote-tracking branch 'origin/blender2.8' into temp-outliner-visibility

Outliner: Gray out collections only when they are invisible

Re-factor of 4521d3e7074d.

Fix/workaround issues in pose and edit mode

[re-committing]

Edit mode was unable to select, pose mode was unable to move bones.

Outliner: Implement 3 levels of viewport visibility

Now collection and objects can be either:
* Hidden for all the view layers.
* Hidden for a view layer but not necessarily for all others.
* Visible for a view layer but not necessarily for all others.

Regarding icons: Whatever we decide to use for the "Hidden for all view
layers" needs to be a toggle-like icon. Because when viewing "Scenes"
instead of "View Layer" in the outliner we should be able to edit the
collection "Hidden for all the view layers" as an on/off option.

See T57857 for discussion.

Per view-layer collection visibility

[re-committing]

We still control this in the viewport collections visibility menu. But
now we are actually changing the visibility of the collections, not of
the objects.

If a collection is indirectly invisible (because one of its parents are
invisible) we gray it out.

Also if you click directly in the collection names, it "isolates" the
collection by hiding all collections, and showing the direct parents and
all the children of the selected collection.

Development Note:

Right now I'm excluding the hidden collections from the depsgraph.
Thus the need for tagging relations to update.

If this proves to be too slow, we can change.

Outliner: eyes for collection affect collection visibility

As oppose to affect the collection objects' visibility.