Repeating timer

[GeckoEidechse]

The idea is simple, when the timer hits zero it vibrates as usual but the timer goes back to the original value it was set to (and optionally auto-starts again).

The use-case would be for exercises that are time segmented, i.e. you have to do exercise A for 30 seconds, then exercise B for 30 seconds, etc.

Naturally, manually setting the value back to 30 seconds after each exercise gets annoying really fast and just interrupts the exercise flow.

Related to #1544