Custom emoji, initial link previews, thread UX

* Emoji/sticker autocomplete (:search)
* Send link previews
* Allow request voice when muted in a channel
* Support SVG (for avatar, image preview, etc)
* Reply to null thread re-use existing thread from other replies
* Make thread auto-follow in channel optional and off by default
* Long press send button to send media
* Fix some RAM usage issues
* Fix custom account colour on notifications
* Fix some file permission issues
* Audo memos in opus where available
* Allow editing or copying autogenerated password
* Onboarding improvements
* Fix bits-of-binary serving