Update timer.models with Timer

Timer is a model for representing simple timers accurate to the second
Add Timer.increment_time(seconds) to add time to timer
Add timer list and detail views to views.py

Add TimerList a generic ListCreateAPIView to display a list of all timers
Add TimerDetail a generic RetrieveUpdateDestroyAPIView to display the details of a given timer
Update timers/urls.py to include timer.urls
Add timer/serializers.py to serialize timers
Add timer/urls.py

Add /timers to list all timers
Add /timers/<timerID>/ to display specific timer:
Add initial migration