Fix sorting of nick/channel lists when upper+lower case items exist.

HtmlList.get() was looking for a value in .nodes based on an untouched
key, but all the keys in that map have been folded to lower case by
.insert(). Fix .get() to lookup the node value by lower-case key.

While here, clean up some of the CoffeeScript cruft from nick_list.js
and html_list.js.