Add rudimentary resting timing and rest/pomodoro alternation
Aborting a break causes the next interval to be a pomodoro
Add pomodoro interval abstraction to handle extra Pomodoro Technique data
Make pomodoro controller use pomodoro intervals
Show start icon instead of restart icon after aborting a break
Remove TBDs from countdown controller; state is right where it should be
Move a TBD about drift to TODO as it may not be a concern