Blender Git Loki

Outliner: Added new mode for displaying "orphaned" datablocks

Orphaned datablocks are those which have either:
* 0 users
* A "fake" user only

In the case of the former, they will be quietly discarded from the file on the next
save + reload. Hence, it is helpful to have a view where you can confirm which ones
fall into this category and might be worth saving.

We also include datablocks with a fake user only so that datablocks given a user
above can have that easily turned off again (in case the user makes a mistake).
Another benefit of showing these is that it become easier to remove fake users from
datablocks you no longer want retained without having to hunt for them.