Disable setting places association for farms.
Enable delete place associations via PUT.

+ Add specs for updating depots.
Enable creating a depot with a places association.

+ Add specs to creating a depot with and without a place association.
+ Remove redundant specs.
Refactor assigning places associations.

+ Use before_filter.
Convert spec into shared example.
Raise exception when places argument is missing.
Update test data to respect the direction of associating places.
Allow depots without farm associations.
Merge branch 'bugfix/places-association-160' into prototype