Consolidate the code copy button
Adding the code code button was done by manipulating the HTML of
the event body to add a span tag, then adding the onclick handler
after the thing was mounted. Apart from splitting the code between
two places, adding the span tag was, according to Chrome's
profiler, taking up quite a lot of CPU cycles (apparently as soon
as you set the innerHTML on a div). Instead, just build the whole
lot together after the component mounts.
