Adopt androidx paging

[ZacSweers]

Resolves #39 Resolves #97 (hopefully) Resolves #59 (hopefully)

Very much a work in progress. This replaces the current StorageBackedService approach with androidx.paging's solution instead. Part of this will require more widely adopting coroutines for this stack, but starting right now with a simple bridge from the Service implementations' rx code to coroutines in paging as needed.

TODO

• [ ] Image services support
• [ ] Finish wiring clicks
• [ ] Figure out empty loading/error states
• [ ] Test rotation support
• [ ] Move Service API to use coroutines
• [ ] Figure out why HackerNews/firebase no longer work
• [ ] Figure out why a refresh always adds one item to the top/moves the list down one item
• [ ] Remove the old ServiceFragment
• [ ] Fix per-service layout theming
• [ ] Test with append-only services (should just use previous data in bottom of list)