Mobile feature parity

[kaavyajayram]

• [x] Adding reacts
• [x] Conversation archival (and archive view)
• [ ] Sending attachments
• [ ] Downloading attachments
• [x] Gallery view
• [x] Conversation options menu (for now on desktop only has clear convo and settings, though)
• [ ] Conversation settings (group and pairwise - set picture, title, color if pairwise, etc)
• [x] Typing indicators
• [x] Per-message expiration
• [ ] Copying entire message text (to the clipboard; nice to have, might involve c++)