Add option to fetch holidays from Google Calendar

While we're working on rolling this into things, it would really be nice if there were the option to include Sunrise/Sunset times for selected days. (i.e. "Display Sunrise times every Tuesday" or "Show Sunrise and Sunset times on the 4th Thursday of each month" or whatever.)

Thanks everyone.

Merged into the develop branch.

Automatically closed - issue fixed for 2 weeks with no activity.