Initial commit for GWT code.

A few quick pointers regarding the build script:
    -   The default "compile" target will run the full GWT compiler.
        This could take a while (30+ seconds) so if you only want to
        compile the H2O wrapper, run the "compile-h2owrapper" target.

    -   For testing and debugging GWT, you can streamline the process
        by running the application in hosted mode. Simply call the
        "run-hosted" target and it will do the rest.

    -   If you run into GWT-related build problems, shoot Nick Ibarluzea
        an email and I'll try to help.