Blender Git Loki

Bugfix 33560

Setup: 2 windows, 2 scenes, shared objects and groups.

Errors:
- editing in 1 window, didn't correctly update shared stuff in the other
(like child - parent relations)
- deleting group members in 1 scene, could crash the other.

Fixes:
- On load, only a depsgraph was created for the "active" scene. Now it makes
depsgraphs for all visible scenes.
- "DAG ID flushes" were only working on active scenes too, they now take
the other visible into account as well.
- Delete object - notifier was only sent to the active scene.

All in all it's a real depsgraph fix (for once!) :) Using multi-window and
multi-scene setups now is more useful.