This commit makes vnc_playback.html functional once more, and completely
refactors tests/playback.js to make it usable in other scenarios.
In order for vnc_playback.js to properly load playback files now, they
must `export` their variables.
setTimeout() is subject to delays, possible massive ones. As such it
is rather useless for performance sensitive code. Use the non-standard
setImmediate() API instead, emulating it on postMessage() when it
isn't available.
This commit restructures noVNC, splitting it into the core directory
and the app directory, with the former containing core noVNC parts,
and the latter containing parts specific to the application.