The eventual goal is to avoid UI-related stanza processing if the relevant chats
aren't in the DOM.
With the current architecture, chatboxes are created (and the stanzas
related to them processed) even if `#conversejs` isn't in the DOM.
* Initial work on making controlbox an element
* Create a shared base class
* Ceate ChatBoxViews proxy
* Update sass now that certain classes are moved to converse-chats element
- 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
