added help functionality to ui by adding a Help model, controller and
command-line view
also added a more general Controller interface that is applicable for
Help and Interpreter controllers
added validation via own Validator class in ui (it wasn't possible to
use OVal because firstly Groovy and AspectJ don't work together in
Eclipse (weaving wasn't possible)) and secondly the non-aspect approach
of OVal can only validate objects, but no input parameters of methods)