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.
-Create application->switchManyWindowsBack() method
-Create equivalent to empty window enum class
-Remove stored prevWindows variables
-Add bottom bar to empty window (equivalent to allEvents)
-Repair going back to previous windows functionality
-Repair switching window (with empty events DB)
-Add EventShift value to event records time