Allow loading more messages in history

[mi5o]

The application displays only very limited number of previous messages. This might be sufficient for many (most) use cases, but the application should be able to (repeatedly) download more messages deeper into history — either proactively, when a user is scrolling and nearing the oldest message available to the app, or upon user's explicit request (via well known pull-down gesture).

Please note that some rooms might have tens of thousands of messages, so some resource management is necessary. Either there should be a hard limit (since the application claims to be bare bones only), or the application should consume very little resources per message, or — similarly to the official Element client — it should drop messages too far from upper or lower edge of screen. The last option would also require a "jump to end" button, to avoid loading all dropped messages again, while returning to the end of the list.

(report based on foss-signed-31.10.2022-V1.apk running in LineageOS)