Replace cityname in indicator id with loop index

Cannot use cityname as those can have spaces/punctuation/etc
that tanks the id selector
Default Indicator.city_name to a string value

...so that we get a display name in the UI.

TODO: Attach a user-customized city_name to the
GTFSFeed object.
Add bulk indicator delete, filtered on fields
Complete Add/Remove City Modal

TODO: Copy translations
TODO: Scenarios

Updates angular translation files
Add tests for django indicators DELETE endpoints

Cleanup comments/logging
Merge pull request #157 from WorldBank-Transport/feature/city-modal

Feature/city modal