[index] Add navbar on top.
[index] Dynamically change quests and sandbox on hashchange.
[index] Add lang and theme dropdowns to Settings.
[cm] Load theme files async.
[cm] Import CodeMirror theme files.

https://github.com/codemirror/CodeMirror
[cm] Import addon/mode/loadmode.js and some mode/*

Modes added: clike, css, django, html, javascript,
markdown, php, properties, python, ruby, scheme,
shell, xml, yaml.
[cm] Load modes async.
[cm] Fix dd-only-line behavior.
[cm] Load modes async.
[help] Fix to accept dgg (operator->partial).
Merge branch 'develop' into sandbox
Merge branch 'sandbox' of origin into sandbox

Conflicts:
	include/nav.js: checking if mode==="text"
	index.html: including clike.js for default.
[index] Open local file.
Merge branch 'sandbox' into develop
Merge branch 'develop'. Add navbar and sandbox feature.
Merge branch 'master' into gh-pages