1. Add surrounding messages to the given messages so we have a full screen of content to make it feel lively even in quiet rooms
- As you scroll around the timeline across different days, the date changes in the URL, calendar, etc
2. Add summary item to the bottom of the timeline that explains if we couldn't find any messages in the specific day requested
- Also allows you to the jump to the next activity in the room. Adds `/:roomId/jump?ts=xxx&dir=[f|b]` to facilitate this.
- Part of https://github.com/matrix-org/matrix-public-archive/issues/46
3. Add developer options modal which is linked from the bottom of the right-panel
- Adds an option so you can debug the `IntersectionObserver` and how it's selecting the active day from the top-edge of the scroll viewport.
- In the future, this will also include a nice little visualization of the backend timing traces
Eric Eastwood