* Indicate obsolete extensions
* Make obsolete indicators red
* Move obsolete extensions up the list
* Add base button theme for holder
* Use red button color state instead of explicit text color
Kotlin: 1.2.71 -> 1.3.50
Coroutines: 0.30.2 -> 1.3.1
Gradle: 4.6 -> 5.4.1
Android gradle plugin: 3.2.1 -> 3.5.0
This brings us down to *one* experimental coroutine API, and we've
opted in to using it in just *one* place.
(The fact that the API to opt-in to using an experimental API in a
specific place is *also* experimental surely will not come back to
bite us later.)
