Convert the Hijri package to a generic Calendar package
Add support for conversion to/from the Jalali calendar
CalendarConversion: use DatesRole
CalendarConversion: update output format.

Also rework the logic somewhat to (potentially) make it easier to
follow.
CalendarConversion: expand test coverage.

Also cleaned up some code to make sure triggering makes at least minimal
sense.
CalendarConversion: update styling.

- New date outputs with per-calendar months.
- More standardized CSS.

I'm less than excited that you can't enter the other calendars with
month names, but that'll have to be ok for now.
Merge pull request #652 from duckduckgo/mwm/jalali

CalendarConversions: now with the Jalali calendar