handle multiple timer states

- feat: separate timer actions from states by adding a new class TimerEvent to hold actions Reset, Start, Pause, Finish, Refesh that could be performed on a timer.
- feat: handle multiple countdown timers in the App file by creating a map of the timer id to the countdown timer.
- fix: use gson instance from  TypeAdapter in Room's Converters class
- ref: remove scroll view parent from each timer item, a fix for the keyboard obscuring a label will be implemented in a future commit

app/src/main/kotlin/com/simplemobiletools/clock/models/TimerState.kt

@@ -2,10 +2,7 @@ package com.simplemobiletools.clock.models
 
 sealed class TimerState {
     object Idle : TimerState()
-    data class Start(val duration: Long) : TimerState()
     data class Running(val duration: Long, val tick: Long) : TimerState()
-    data class Pause(val duration: Long) : TimerState()
     data class Paused(val duration: Long, val tick: Long) : TimerState()
-    data class Finish(val duration: Long) : TimerState()
     object Finished : TimerState()
 }