Add ability to create/edit custom location data

@twymer
http://manage.dimagi.com/default.asp?147344
QA Passed!
It'll be hard to annotate directly, but basically the bulk of the changes are [here](https://github.com/dimagi/commcare-hq/commit/a46e1f027fb3ec7f0b1c02357fec089071026326).  There were a couple things that would have to be calculated per-location but shouldn't, so I moved some of the functions used in import to the importer class.  The diff is easier to read [with whitespace ignored](https://github.com/dimagi/commcare-hq/commit/a46e1f027fb3ec7f0b1c02357fec089071026326?w=1)