#92 completed menu entry

[Linas Vepstas]

The top-level "timer" menu entry currently has start/stop choices in it It should also have a choice "task completed" which not only stops the timer, but also changes the task status to "completed". (right?)

Meanwhile, in the properties menu, marking a task as "completed", "cancelled" or 'on hold" should have the side effect of stopping the timer for it. (i think this is a good idea, right?)