Use a better naming for argparse helper.
Move dns check to the backend.
Replace twisted's callLater with Qt's singleShot.

Note: we use an alias for singleShot called QtDelayedCall.
Merge remote-tracking branch 'refs/remotes/ivan/feature/more-app-cleanup' into develop
Move backend to its own namespace.
Move Signaler to its own file.
Move backend's components to its own file.
Merge remote-tracking branch 'refs/remotes/ivan/feature/split-backend-components' into develop