allow undelete from activity stream

[putt1ck]

The quickest/easiest place for someone to undelete an item they just accidentally deleted (or just realised they might have accidentally deleted) would be in the activity stream.

While in a small/low activity installation the deleted files area would be similarly quick, it doesn't scale at all well, getting slow (minutes to load) once file count passes 100k and failing completely sometime around 500k (we're working on a "Trash+" to alleviate that).

Even if trash was scaling, it would still be easier for an individual user to look at their activity stream to locate and undelete the deleted item - particularly as it might be the first place they look when they can't find it.