06-navigation

[Serchinastico]

This PR is not meant to be merged

This is how to use the Navigation component:

• Transform all activities into fragments as navigation components are done with a fragment manager under the hood. No big deal with lifecycle methods, the layout is inflated on the onCreateView method and we update the binding on the onViewCreated.
• Define navigation between screens inside the navigation_graph.xml resource file. It defines input arguments and with the safeargs plugin we automatically create classes to navigate through fragments.
• Include the new fragment testing library so that we don't have to create an empty activity ourselves. I opted for this solution because reusing the MainActivity for testing purposes was making tests crash. We are losing the toolbar checks as we are now showing an activity with only the fragment.