Removed es6 prompt

[tyllrb]

Not sure if we're completely removing support for sub ES6 javascript flavours? If so I can delete the es6 conditionals in templates/sections/bigwheel/normal/index.js and templates/sections/preloader/index.js, as well as any other conditionals relating to es6 wherever they may be.

[njam3]

@tyllrb Yeah, we want to remove all references to the useES6 prompt, so anywhere you see {{useES6}} or gen.config.get('useES6') you would want to remove the conditional and leave the code of the true conditionals. We basically want to have the templates reflect a useES6 = true state.

[tyllrb]

cool 👍 updated the PR -- got rid of any conditionals relating to whether or not ES6 is true or not, also the index.js files in templates/sections/bigwheel/* now use classes instead of extending the function prototype namespace.