Blender Git Loki

Outliner: Use restriction columns in "Orphaned Datablocks" view to manage usercounts

When in "Orphaned Datablocks" mode, the restriction columns are used to display
usercount indicators and toggles to manage whether datablocks get saved or not.

* The first column shows an icon to indicate whether that datablock is going to get
saved. A tick indicates the datablock will be saved, while a cross indicates the
opposite. Clicking on this changes whether the datablock will get saved.

* The second column shows the usercount.

* The third column shows whether the datablock has a fake user.


Notes:
* The second and third columns are pretty much redundant (functionally speaking).
While it is possible to also toggle fake users by clicking in the third column,
its role here is more as information for power users (and hopefully to allow others
to connect the relationship between the saved/not saved status and fake users)

* I'm not sure whether the use of the X here for the "not saved" state stands out enough
to draw user's attention to items which are "in the danger zone".