define Loader.define(name, src)

Fixes #729

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/732

Closes #732, closes #729.
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.
reformat system-map file
Remove commented code and Traceur -> traceur; rebase