Use browserify with babelify for front-end JavaScript

[marcobiedermann]

I suggest switching from concatenating JavaScript files to use a module bundler like Browserfy.
This way we could manage our dependencies more easily.
In this addition I suggest using some of the new ES2015 syntax features which will improve our code over all.

[stefanjudis]

Only when you compare the files before and after. ;)

Perf-tooling is neither a complicated thing nor are we shipping with a lot of JS or use heavy dependencies. Introducing browserify usually comes with additional "module" code (haven't used it very often though).

I have no idea - but currently we're shipping 7k JS (not gzipped). I'd like to see the change in size first, if that's okay. :)