Rename elapsed-limit to state-duration
Use 'double' type to store time
Fix building sound file uri
Calculate elapsed time on request

This replaces some operations with timestamps, removes redundancy between _elapsed and the timestamps, and in theory has better accuracy. _elapsed property is now used as delta parameter, in case we wish to express that there were interruptions during current state.
Minor text string fixes
Reduce text shadow of screen notification
Fix notification icon being multiplied
Remove empty line from notification