various

- Refactored generics and methods in DataBase/DataAccess (removed type
explicit methods, as this concept would have resulted in way too much
methods and increased complexity)
- Made Task abstract and added class GeneralTask for improved type
savety and error-proof "select by type"
- Refactored some Lists to Collections (added custom Collections
interface)
- moved jqueryTreePlugin.jsp (scriptlet) call from javascript to
controller method