Remove internal modules and move all module code into modules.js

This removes the special case for internal/standard module names.

To get this working runtime/url.js and runtime/module.js both export their functions to the $traceurRuntime object.

All the System code is now located in runtime/module.js instead of being split up between runtime.js and module.js

Review URL: https://github.com/google/traceur-compiler/pull/526

Closes #526.