Add Use Cases for trips stuff

[dellisd]

This restructures the Trips feature to use the UseCase pattern for passing data between the repository and the viewmodel. On top of this, it also now uses Flow from Kotlin's coroutines library to allow the viewmodel to react to updates to the cached trip data in the repository.

This also updates the Kotlin Coroutines library to 1.3.0-M1.

Checklist

• [x] I ran ./gradlew test connectedAndroidTest detekt
• [x] I rebased off of upstream/master
• [ ] I added tests if applicable

[GustavoSanMartin]

I know it's already large, but you should really add tests in this pr! Going forward, all our PRs should add tests.