Timer callbacks

[dancheskus]

onTimeUpdate wrong triggering time

onTimeUpdate function is called on component mount. I think it should be called ONLY when timer status is 'RUNNING'. Otherwise there should be some checks like:

onTimeUpdate: () => {
  if (timerName.status === 'STOPPED') return;

  ...code
},

Good callback fn to add

1. onTimeReset
2. onTimePause
3. onTimeStop
4. onTimeStart