location fixture support in app builder

there's some semblance of a spec here: https://docs.google.com/a/dimagi.com/document/d/1n6CI725XA5eJ0p8Vt-PMBz_8yyZ1EZDwmhwGtMUBYOw/edit

the tests are more accurate in terms of the behavior though.

basically allows you to type: `location:type:reftype/property` and reference the location fixture in the app builder. so you can query commtrack parent names and other types of things