Feature: Set start/end date for all calendar entries

[landonreed]

A common issue encountered when editing feeds from some other source is that there is not a good way to bulk edit calendars for a feed that has expired. Some GTFS feeds have many calendar entries (e.g., one per route) and it is tedious to attempt to update each calendar end date one by one.

We should probably come up with a framework/endpoint to do this in a generalizable way. E.g., a PATCH endpoint in EditorController.java that uses something similar to Postgrest to select rows to edit and contains a JSON object with the fields that should be updated:

PATCH /calendar?end_date=eq.20190931 HTTP/1.1

{"end_date": "20191031"}