1. Prepare Pure and Bell specific `Application`
classes and add them to `app` target:
- `products/BellHybrid/apps/Application.cpp`
- `products/PurePhone/apps/Application.cpp`
2. Update `CMakeLists.txt` files.
3. Move `ApplicationBell` implementation to Bell-specific
`Application` class and remove `ApplicationBell` files.
4. Change Bell apps parent classes from `ApplicationBell`
to Bell-specific `Application` class.
5. Rename `Application` to `ApplicationCommon` in the rest of the files.
The following commit provides implementation of ProgressTimer.
The timer purpose is to provide suitable abstraction of a timer
that can be visually represented by both Text and Progress.
The implementation is based on MeditationTimer and thus
the ApplicationMeditation's part that uses MeditationTimer
has been refactored.
