GWT Preloader + Cleanup + Reflection

Improved GWT preloader with continuous byte progress and audio preloading. Cleaned up code to use XmlHttpRequest 2 binary downloads.
- Create a new class AssetLoader that implements all type of asset loading
- Directly download binary content through XHR2 ArrayBuffer (instead of String + overrided mime type)
- Refactored progress report to use a global preloader state with continuous download progress (based on byte progress / total byte size)

Add capability to extend GWT reflection system with module configuration property.
- define 2 simple properties to include or exclude classes from reflection system