Events take a long time to load

[joh]

Fetching the events from Google Calendar is rather slow. This is especially true when there are many calendars: for each calendar, an HTTP request is made. Typically 4-5 seconds pass before the events pop up in my GNOME Shell calendar.

At the moment we update the list of events in the following cases:

1. When the month requested is not in the cache
2. When the calendar requests a refresh by force_reload=True, which seems to be whenever the calendar is opened by the user.

Suggestions:

1. Pre-fetch events from a few months before and after the current date.
2. Ignore force_reload and instead employ a time-based refresh, e.g. every 10 minutes.