Cyclic imports

This changes our setup to use [es6-module-loader](https://github.com/ModuleLoader/es6-module-loader) for loading files.

It also adds dependency on "systemjs" which is something like RequireJS implemented on the top of the ES6 module loader API. I hope we will be able to get rid off that dependency but we need to change Traceur to generate different output.

Next thing is to change annotations to make it work with cyclic dependencies.

The last commit is not supposed to be merged, it's just an example that the cycles work.