Improve performance, especially on timeline

RiotX may suffer from ANR after several navigations between rooms.

Also it consumes too much RAM. Let's see how we can improve that.

Several ideas:
- [ ] fix memory leaks if any
- [ ] use another Adapter for the timeline, Epoxy is not well adapted to infinite list
- [ ] explore new things from latest Jetpack release: https://www.youtube.com/watch?v=R3caBPj-6Sg&list=WL&index=27&t=0s and https://medium.com/androiddevelopers/whats-new-in-jetpack-1891d205e136