Fix activity entries for docs connected to groups

Hi Boone,

This pull request addresses a part of #338 - new docs not appearing in group activity stream.

When a doc is created and is attached to a group, the corresponding activity entry is not properly recorded into the group.

I'm not too familiar with BP Docs, so my fix is kind of a workaround.

See my commit comment in 8ec8f03 for full details.

Currently, this pull request doesn't support doc comments being recorded into the group activity stream yet.  Ran out of time, but if I fix this before you merge, it'll also be in ths pull request.  Will update this request once I've looked into it.