Groups filter hack for smaller groups listings

Groups filter hack for smaller groups listings

This change is a dirty hack that lets site admins filter the "Contacts
Group(s)" field output in select profiles. This reduces overwhem for
users when they are making a donation or filling out a form with the
Groups signup field. This is preferable to using a custom field with
smart groups because the Groups field provides double opt-in, while
custom fields do not.

The filter is controlled via a json string stored in a drupal variable
that can be set with drush like so:

drush vset --format=string groups_field_filters "{...}"

See the documentation marked with "sudoman hack" in
CRM/Contact/Form/Edit/TagsAndGroups.php for an example.