lib/system-map.js from https://github.com/guybedford/systemjs.git.

Copied at beae8195d. License MIT.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/726

Closes #726.
Use system-map to map tracuer module names.
Convert system-map.js into es6 module exporting applyMap.
Apply map to System.normalize().
Change import specifiers in repl to load out of bin/traceur.js, not reccompile traceur.