Rename Features to Views and Screen to View

[mbernson]

The folder name "Features" is vague. What does a "feature" consist of? In practice, it's mostly views and viewmodels that go in this folder. So why not rename it to "Views"?

Also, we copied the naming of a "Screen" from the Android template. But SwiftUI doesn't really have a notion of a screen. Let's rename them to *View and their content view to *ContentView.