this linked_locations thing is no longer being used
move bind_to_location to the only place it's used and simplify
replace reference of location_[-1] with location_id (which is equivalent)
duplicate location_id in case it's not set
remove code that couldn't possibly have been working

get_product_case was removed from requisitions long ago
more impossible/broken code
set location_id in addition to location_
replace more references of location_[-1] to location_id
Fix test
Add a ton of tests
Use new location_id in couch view
Switch signals to use location_id
Remove location_ rebuilding
Merge branch 'master' into reduce-location_
Remove location_ from ES
Switch case model to location_id
Merge pull request #4559 from dimagi/reduce-location_

Reduce location