Implement activity timer

[Woyken]

Activities can have timer, just like nursing/pumping/sleeping
in the app you select activity type and start timer,
in the edit you can only add note, start_time and duration

actions:
Start
Pause
Resume
Complete
Cancel

If you click on another activity prompt shows up if you would like to change activity, and the timer will now be associated with the new activity type

let's not do activity switching for now, just the regular timer things