Icons from https://feathericons.com/

now that each message has its own id and feedback is related to this, we
can allow feedback for any previous message.

Because we do post-processing of the LLM response (e.g. replacing tags
with links) it is difficult to handle streaming, so we give it up
completely.

It was getting unwieldy to modify;
also the combination of html+css+js meant it was hard to edit it
(syntax highlighting, comments, autocompletion etc.)