Make loading of Babel configurable

[Daniel15]

Babel is pretty large (~2 MB). If the user has already transformed their JS (eg. through Browserify or Webpack) and only uses AddScriptWithoutTransform, we don't need to load Babel at all

• Add config option (eg. LoadBabel or something)
• If AddScript is called but LoadBabel config option is disabled, throw exception explaining that it won't work