Several of the major browsers now natively support modules, so we
only need the converted modules to handle older browsers. Make sure
it's only used when necessary.
This changes around `utils/use_require.js` to be able to generate any
of AMD (RequireJS), CommonJS, SystemJS, or UMD modules. The three
former also include support for translating `vnc.html`, producing a full
"app" version of noVNC.
Juanjo Diaz
Pierre Ossman
Solly Ross