fixes to the project structure to make it easier to contribute

I removed the eclipse project files and fixed up some things in the pom.xml. This makes it possible to use the project as a maven project, that can be imported with the m2e plugin for Eclipse.

This should be better than simply uploading .project and .settings, as .project and .settings are often specific to one computer and therefore hard to share and often cause merge conflicts.

Additionally, when only using maven, it would no longer be neccassary to include the libraries in the repository. As however ant is also supported, we still need to ship them. If ant support gets dropped, the lib directory can be removed, as maven is able to automatically fetch the dependencies.

Instructions on how to use maven with Eclipse are found in CONTRIBUTING.md