#219 Attaching colours to calendars

[NWoolridge]

There should be a way to attach an event colour to a particular calendar,
so that when the user switches from the (default) all-combined view to a
particular calendar (eg. "calendar 1"), the calendar colour remains the
same colour it was in the "All-combined" view. Currently, the calendar
switches any individually viewed calendar to the "event-1" colour, which is
confusing for users switching between multiple relevant calendars.