[mkcal] Add command line tool mkcaltool for resetting alarms

The command

  mkcaltool --reset-alarms <notebook UID> <event UID>

will reset the alarms for the event in the specified notebook.
[mkcal] Program timed alarms to use mkcaltool to reset alarms

If an event has alarms and is recurring, program timed to use
mkcaltool to reset alarms when timed alarms have been served.

The timed whenServed flag indicates that the command associated to
a timed action will be run when an event is triggered or missed.
[mkcal] Observe alarm offset when calculating next alarm time