Save address fields when plots are moved

Includes the following places:
* Create a new tree on map page
* "Quick edit" on map page
* Edit details page

This introduces a transitive dependency where editing will fail if the
user has permissions on plot.geom but not on plot.address_*.

Fixes #341
Merge pull request #850 from ahinz/fix/341/reverse-geocoding

Save address fields when plots are moved