In order to add a toolbar with a back button in settings I needed to extend from a fragment
so I converted SettingsFragment into a fragment and created SettingsContainerFragment,
the latter is injected as a child of SettingsFragment inside a FrameLayout.
Since SettingsContainerFragment extends from PreferenceFragmentCompat, this allows
to swap it for other and, in the bigger picture, allow an arbitrary organization.
