Display recurrence summary in event info, event editor: Bug #732930

RecurrenceRule can now explain itself as long as the RRULE is simply
defined.  (California will never produce an RRULE it can't explain.)
This explanation is now displayed in the event popover, the main
editor pane, and the recurrence editor as a guide for the user.
Mention webcal in activator list: Bug #736087
Use word-character wrapping for event description: Bug #736088

Also a slight increase in the description window size.
More debug
Merge branch 'master' into wip/732671-double