Initialize ViewModel EventDispatcher in NavigationView constructor

[danesfeder]

Closes #920

We were previously waiting to pass the NavigationViewEventDispatcher from the NavigationView to the NavigationViewModel when navigation is initialized. When can do this much sooner though, right when the NavigationView is inflated. This also removes the need to set it to null in the view model to prevent a leak. 🎉

[devotaaabel]

How does this prevent the need for setting it to null to avoid leaks?

[danesfeder]

@devotaaabel the NavigationViewModel survives rotation, but the NavigationView itself is destroyed and recreated, so setting the dispatcher to null originally prevented a leak because the view model would no longer hold onto the old reference of the dispatcher. With this PR, the viewmodel dispatcher reference is updated immediately, as soon as the NavigationView is created, so no more leaks

[Guardiola31337]

Minor comment not blocking the PR though.

[Guardiola31337]

For consistency, could we rename init methods to initialize? Saw that we're using initialize nomenclature in navigationViewModel for example.