This PR provides implementation of home screen notification for
`notSeen` messages received from a single number. The "single-number:
`notSeen` message notification distinct from "multiple-number"
notification with the following features:
- displaying formatted contact name
- `onActivated` it switches to respective thread window (instead of
all thread window) in `ApplicationMessages`
The PR also introduced some `ActiveNotificationsModel` code refactor
to align the implementation with `Single Responsibility Principle`
