If a message comes in after joining the MUC but before the MAM messages
have been fetched, then converse-mam will query for MAM messages newer
than that message, causing an empty history (except for that one message).

It's currently only used by the MUC header to render URLs in the subject

- Don't replace entire textarea when entering a second emoji
- Focus emoji picker on tab completion when it's already opened

for emoji related data

Fixes #2126

(i.e. not on reconnection)

the first time it's opened

Changes how rich message markup is generated and kept track of.
We now have a MessageText class which subclasses String and which keeps
track of the rich markup associated with the message.

Wait for emojis to be initialized before parsing MAM messages

- Declaratively render the emoji picker dropup
- Got rid of converse-emoji-views
- Adapt OMEMO to the new buttons stuff
- Make emojis json global, to try and speed up tests
- omemo: Move functions to the top of the module