Update of Force Chat example to work with new version of Force Webserver and DartVoid

Created a more clear directory structure. Added some more comments to server.dart.

This is mostly just directory structure changes and a app.yaml file. The call to ForceServer() is changed because Force has change a little bit to use the changes of Force MVC's webserver. 

Concerning the directory structure, it is both because DartVoid requires it but also because the structure inherited from pub is not really designed for applications, it's designed for packages and I don't think it's optimal. I have not run pub build when I have tested but I don't think it will be a problem either. I think you should be able to run pub build and then set the "clientFiles" parameter to point on the build directory. For development on localhost though it's a lot easier to just run server.dart like this example does and you get a better and faster development loop I think.