Hook up Javascript implementations to JSAPI class

To enable this to work, developers need to modify the default index.htm generated by Protobuild to have:

        manifests: [
          "MonoGame.Framework",
          "JSILPort.exe"
        ],

This will cause the appropriate MonoGame libraries to load.
Merge pull request #2517 from hach-que/web-api-working

Hook up Javascript implementations to JSAPI class