Add Umm al-Qura calendar support

[ddohler]

This is an Islamic calendar used in Saudi Arabia, and it gives dates that are sometimes a day offset from the Islamic calendar calculations in this library.
https://github.com/tytkal/python-hijiri-ummalqura

[fitnr]

If that library is working, I'll mark this as "nice to have, not a priority".

[ddohler]

It works as far as I've tested it; it would be nice to have together in one library with other calendars, but the other library should be workable for our use case for now since Umm al-Qura is the only non-Gregorian calendar we need to support at the moment.

In the (probably unlikely) event that we have time for implementation, would you accept a pull request for equivalent functionality here?

[fitnr]

@feenes It has not been merged. The item above your comment refers to a different library.

[snoopyjc]

I'd like to see this support too, in order to match the [$-1170401] number format of Excel.