Prefix RQDA files with the OG group name

[tanius]

Texts (called "files") cannot be grouped in RQDA, makeing it quite hard to navigate them if there are many.

One way to help navigating RQDA files would be prefixing them with the name of the first (=main) Organic Groups group that the corresponding node or comment was part of in Drupal. Alternatively or additionally, group membership could be encoded into automatically exported pseudo-tags (only created on-the-fly for exporting).