Fix ElasticSearch bug
Actually save FPRule after modify counts

refs #6611

Use Django's F() construct to update the counts in a way that avoids race
conditions from several instances of the same rule running at once.
Transfer: Only display zip files for Zipped Bag transfer type

refs #6885

Use default filter for DirectoryPickerView which only displays folders
for most transfer types.  If foldersOnly is not set, use a custom
filter to display zips.  Set foldersOnly based on the transfer type.