Use dark purple color background instead of image
Merged PomodoroTimerService, NotificationService

- Moved methods and constants from NotificationService into
  PomodoroTimerService. Now it handles alarms as well.
- Deleted NotificationService.
Renamode PomodoroTimerService to PomodoroService
Renamed PomodoroTimerListener to PomodoroListener
More events notified through PomodoroListener

- More methods (events) added to PomodoroListener.
- Instead of acting directly after a UI interaction, CherryBerryActivity
  just sends the action to PomodoroService.
- PomodoroService then notifies its listener when given these actions.
Moved InternalTimer to CherryBerryActivity

- Count down timer is now completely managed in CherryBerryActivity.
- Timer is started/stopped according to events received from
  PomodoroService.
Timer ticks no loger through PomodoroListener
Removed listener from InternalTimer
Added Session interface

- Added Session interace, which gives information about the current (or
  a given) session.
Added SessionImpl, implementation of Session

- Added SessionImpl class, which implements Session while adding setters
  and other methods.
Added PomodoroServiceInterface, for binding

- Added PomodoroServiceInterface interface, intended for being
  implemented by PomodoroService.
- This interface represents the public interface of the service, mainly
  for the purposes of service binding.
- PomodoroService does *not* yet implement PomodoroServiceInterface.
Use SessionImpl internally in PomodoroService

- Use a single SessionImpl field instead of the status, timerStart and
  timerEnd fields.
- This was just a drop in replacemente; no further changes have been
  made.
Added a getSession method to PomodoroService
CherryBerryActivity uses getSession

- Use getSession where appropriate in CherryBerryActivity.
- This was just a drop in replacement; no further changes were made.
Removed getSession, use session.getSession

- Removed the getSession() method from PomodoroService.
- Use session.getSession() directly instead.
Removed getTimerStart, getTimerEnd, use session

- Removed getTimerStart(), getTimerEnd() methods from PomodoroService.
- Use getStartTime(), getFinishTime() from Session directly instead.
Removed continuePomodoro, continueBreak methods

- restoreState() no longer calls continuePomodoro() or continueBreak(),
  since once the state is restored there's nothing else to do.
- Removed cotinuePomodoro(), continueBreak() methods from
  PomodoroService.
Folded several methods into updateSession

- Folded startPomodoroTimer(), startBreakTimer() and startTimer()
  methods into the new updateSession() method in PomodoroService.
- These methods used to do more, but now the only updated the session
  information.
Added setListener to PomodoroServiceInterface
PomodoroService implement PomodoroServiceInterface

- PomodoroService now implements PomodoroServiceInterface.
- Missing methods (cancelPomodoro(), skipBreak(), cancelBreak()) have
  been implemented as simple calls to stop() and skip(), without further
  changes.
- Added @override on existing startPomodoro(), startBreak() and
  setListener()  methods, updated their comments.