[GTFS Full Support] Add support for calendar dates

[jamespfennell]

• Add a new table to store the contents of calendar_dates.txt and frequencies.txt.

• Will need to create dummy entries in scheduled_service for services that don't appear in calendar.txt.

• Will need to update service map trip filtering for "weekend", etc.

• Smoke test using LIRR, which currently doesn't work because of this.

[jamespfennell]

For service maps, the algorithm probably should be:

1. In the service object, if any of the days are true, then use those days as truth and continue.

2. Otherwise, essentially calculate a histogram of days coming from calendar_dates.txt. Days appearing more than 10% of the time (say) count as true days. Should validate this with the LIRR.

[jamespfennell]

Data persistence has been done, need to update service map logic before closing out.