can choose duration of talk

at the launch of the application, user is asked for the duration of the talk.
Once it is set, the countdown start.
coherent naming of variable

variable are camel case
global variables are prefixed with _
put constant definition in a file
can choose time of the first alert
some refactoring

rename handle method
separate methods to be more readable
add vibe pattern in the CountDown struct
no more use of global _countDown outside of pebble handler
Move CountDown definition into separate files