Basic wiring of Closure compiler

- The compiler pass on all piskel code (some libs are excluded but pass as well, easy to change later)
- The compiler output is currently not used, we just use the validation ability of the compiler. It should be probably pretty easy to not use uglify grunt anymore and move to the SIMPLE_OPTIMIZATIONS if we want to.
- The compiler still emits warnings for the fake @provide & @require we used all over the code. We should probably, in a next branch, remove them and replace them by stub versions of goog.require & goog.provide.
- The code is currently either not or incorrectly annotated.