Upgrade to codemirror 3.0

[iros]

[marijnh]

I just spent some time looking into a hang 1 that was caused by accidentally using CM3 with deck.js-codemirror. The main problem seems to be that deck.js has some overreaching css rules, such as killing the margins and paddings on everything within .deck-container, using a rule that is more specific than a direct class rule, so overriding CodeMirror's css rules, even when they are included after the deck.js css files.

I'm not really keen on adding !important to all the rules in codemirror.css, especially since that'd make it a pain for others to work with, but you may have to deliver a version of codemirror.css that does just that with deck.js-codemirror (or convince the deck.js maintainers to get their css act straight).

Beyond that, I think the only thing you'll have to for this upgrade is to move the sizing css rules to .CodeMirror (not .CodeMirror-scroll), and maybe a few other minor css tweaks.