This removes the special comment part of the ES6 module syntax,
opting to enable ES6 module syntax by default.
It also appends `.js` to all import paths to better support in-browser
loading.
Anyone with basic knowledge of CSS will easily figure out how to
customise the appearance of the UI, so remove the burden of having
to maintain these extra style sheets.
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.