Rake db:import:reservoirs loads data from the CDEC.

- db:import:reservoirs task screen scrapes and populates reservoirs (idempotently).
- current supply now be empty if the data isn't there.
- current_supply_captured_on notes the date of the measurement.
Grab lat/lon for each reservoir.
Include an error message if the reservoir does not save.
Only include reservoirs that have latlons.
Merge branch 'features/import-all-reservoirs'