WPF Designer Fixes (App.Xaml support, Load of AdditionalDlls,...)

- Parse of App.Xaml
- Better Finding of Additional DLLs
- Parse of Frameworktemplates wich have References to Parent Resources (not yet App.Xaml Resources)
- Fixes in Xaml Parser (Attached Events, Attached Properties not always have both, a Setter and a Getter)