GWT:Refactored preloader for improved progress report and audio
preloading.
GWT:Cleaned up code to use XmlHttpRequest 2 binary downloads.
GWT:Add capability to extend reflection system with module configuration
property
Added infos in the CHANGES file.
Renamed AssetLoader to AssetDownloader to avoid having 2 classes with
the same name in Gdx.
Set download size of audio file to 0 when not using browser cache (they
are not preloaded but directly loaded by the audio system).
Merge branch 'master' of https://github.com/vbousquet/libgdx into vbousquet-master