Fixed up project

Hi Petra,

This fix consists of two commits:

1. I've removed all the files that get generated by the build and added them to the .gitignore file so they don't get added back by accident. These should not be tracked in the version control system.

2. I fixed the errors that were preventing the project from working. The specific problem you were stuck on was the fact that the App class was abstract. The App class is an Entry Point to your application, and classes have to be concrete or they can't be instantiated. There were other errors in the App class as well as the pom, the web.xml files, and others. This is all fixed now so you have a working project to start from.

Have fun!