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.
Reworked AppSettings handling of BT devices to be prepared for
handling the HFP profile, eliminating by the way few bugs and
speeding up the flow (by getting rid of few refreshes).
Added unit tests for handling the BT devices flow
Display and keypad setting cleanup. Moved settings window
Names to separate file. Added selective build options.
Fixed SpinBox arrows position. Fixed focus on window start
in InputLanguageWindow and KeypadLightWindow. Moved AutoLock
to Security. Disabled not working options in UI.
