Add hijri_date gem to Gemfile.
Render current month name and year on the page.
Render calendar for current Islamic month.
Use rspec to test all the things.
Move calendar month calculation into a presenter.
Add test for Calendar presenter.
Refactor CalendarPresenter into MonthPresenter.

* Old CalendarPresenter is the new MonthPresenter.
* CalendarPresenter now presents an entire year.
* CalendarController performs date conversion.