Delete BaseX default stuff and integrate maven

These commits remove a lot (but not all) of BaseX default stuff which we don't need for this application.
Additionally, it integrates Maven as it simplifies deployment a lot (at least for me). Being in the `deploy/webapp/` directory simply run `mvn jetty:run` to get Jetty and baseX up and running listening on `localhost:8986`. It uses the users home directory as base path for BaseX, if you want to modify that simple set it your desired value for `basexDir` in the `pom.xml` configuration file.