Use default context sort order when returning autocomplete

Fixes [#1403](https://www.assembla.com/spaces/tracks-tickets/tickets/1403) by greatly simplifying the SQL query.

I'm looking for feedback on this one. This method was doing a lot of work so that contexts with actions were ordered before empty contexts. I'm not sure why this is desirable, so I simply removed that calculation and instead return the contexts in their default sort order. Thoughts?