04-live-data-and-view-model

[Serchinastico]

This PR is not meant to be merged

This is how to use LiveData and ViewModel components:

• Replace old presenters by the new Androidx ViewModel compoments. They are created through a ViewModelFactory that we are redefining just so that we can inject our own dependencies on them.
• All visible properties of view models are now LiveData. That means that they can be observed by the UI and update them on the fly when editing.
• The async model has changed now that we are using LiveData in all layers. We now call our use cases on the UI thread and do the context change on data sources only when required. LiveData has really strong prerequisites to work with it and the threading model is everything but crystal clear, so we are playing it defensively by always posting values instead of changing them right away and keeping ourselves as long on the UI thread as possible as some functions like addSource from MediatorLiveData will behave oddly otherwise.

[tonilopezmr]

Well done 👍

[davideme]

🚀