Double enter groups that are both reporting and sharing groups    

Addresses this comment: http://manage.dimagi.com/default.asp?132165#BugEvent.743280

We want groups that are both reporting and sharing groups to appear twice in the list of groups and also for the filter to behave differently depending on which entry in the list you choose. Therefore, adding `g__<group_id>` to the url no longer conveys enough information. Therefore, I've added another type of string, `sg__<group_id>` for sharing groups.

This also required reworking the `EmwfOptionsView.get_groups(start, size)` function. Because the group query is paginated, and a group that is both a reporting and sharing group might show up on different pages (once for being a reporting group, once for being a sharing group), I was forced to turn this into two separate queries. There might be a way to do this in one query, but I wasn't able to figure out how.

Note: This PR requests a pull into caselistmixin-refactor, not master.
Does this sound right to you @esoergel ?