Add interval timer feature.

[Andrzej M.]

As suggested I'm reporting this as a bug, but it's rather a feature request. I'd love for Hourglass to have additional tab / modified timer tab for interval timer which is really useful while excercising (running / cardio training). It should provide an input filed for number of rounds, round and break lengths. A notification (preferably a sound notification) should be sent at the start and the end of each round. Hopefully the description is quite clear. In case it's not, I would like it to be similar to this website: http://www.intervaltimer.com/create/round-timer