Use the sidebar to sync DM messages instead of visiting the DM itself,
so as to not make LINE (and your contact) think you really read the DM.
This cannot be done for non-text messages (which are not previwable in
the sidebar) and non-DM chats (whose sidebar messages don't say who sent
a message).
- Handle "decrypting" state of messages
- Handle lazy loading of emoji
- Better handle lazy loading of images/stickers
- Improve reliability of message sending, especially when sending
several messages quickly
- Use m.sticker events for inbound stickers instead of m.image, and add
a config to optionally use m.image if desired
- Use proper sizing for emoji, and add config to scale them since they
are somewhat small
- Deduplicate stickers as best as possible (works until they get a
different blob URL)
- Add config to disable bridging stickers/emoji
- Send m.notice for inbound messages of unknown type
