gitignore symlinked admin media directories
2005: make sv visibility[_override] list_editable

This makes testing visibility changes way easier, because you can just flip the
switches all at once instead of editing every version individually.
2005: refactor and rename unpublish methods on models

The docstrings were incorrect.  This just cleans things up a bit before we hook
up the forms and such.
2005: don't allow unpublishing of already-deleted versions

That doesn't make any sense anyway.
2005: fix frontend form text to match what actually happens
2005: sl.language is now sl.language_code
2005: refactor unpublish view to handle deletion

Also pretty much rewrites the way tasks are created after unpublishing of any
kind, because now that we can delete it's just easier to look at the resulting
state and figure out what to do instead of looking at the action we performed.

This is a really tricky thing and there are probably bugs, so be careful.
Merge remote-tracking branch 'origin/dev' into dev
Merge remote-tracking branch 'origin/dev' into dev