Issue 2221 redux manually reset taggings count

I think for this one it's actually worth reopening:
https://code.google.com/p/otwarchive/issues/detail?id=2221
because it was never implemented as requested before.

Now it is, except that instead of a button there's a ticky box, like @sarken suggested.

Also fixes the wide unicomma for bookmark tags, because hey, while I was in there. (I was trying to reproduce the steps for the taggings_count bug, which would have involved editing of bookmarks, so I came to examine the bookmark model where the tags get created.)
Oh, what the heck, I'll never learn if I don't ask: what does this do?