Modernize JS/node

This is just a wishlist for now, I consider tackling some of the points when I have downtime. As jking3 proposed, these incompatible changes would live in separate "js2" and "node2" directories. Feedback and additions are welcome!

• De-duplicte implementations of JS and node, including:
  • Thrift.TJSONProtocol
  • Thrift.MultiplexProtocol
  • Thrift.Type
  • Thrift.MessageType
  • various Exception types
• Drop support for synchronous service calls (js+node), jquery based calls (js) and maybe even async "callback as last argument" calls; embrace Promise as return value
• integrate JS with "make cross" test suite, possibly using karma and chrome-headless, drop grunt/phantom-based test workflow
• Bonus: publish smaller npm packages for browser and node, which include only the lib