WebComment: UI & backend for bibdoc association

* Upgrade script for new table cmtRECORDCOMMENT_bibdocfile.

* Added some more skeleton for the actual comment-bibdocfile association.

* Interface to associate comment with file roughly done, need to add
  logic for submitting the comment.

* Selection is available from the web interface and the
  selected file is now saved as an associated file to
  the new comment in the database.

* Filtering by file is now implemented, combined with text query
  in comments, better styling is still required.