Add support for Google's Closure Compiler (revisited)

Just throwing it out there... JSMin is old and I ended up removing it from my system after realizing it broke my js for the umpteenth time.

A previous issue (for 6.x) requested to have the "Google Closure" module integrated into advagg, but that was several years ago. Just seeing if this is worth re-addressing or of the original request is still the defacto. I'm thinking it would be nice to use a some compression code that is designed around this decade of web ;-)

https://drupal.org/project/closure_compiler

https://developers.google.com/closure/compiler/