1-second timers available with custom data

The `MyTimer` class holds a message and how many seconds are left in the
timer for the countdown process. Currently showing some basic
functionality and I'll probably change everything in the next commit,
but hey, it works.
Better names and methods for CountdownTimer
Separated countdown class and specialized class

I.e. there's a special countdown MyCountdownTimer for usage in the
Quick-Countdown application and a more general CountdownTimer for other
stuff.