improved kernel implementation documentation (package.html and javadoc)

...rtiss/tooling/kernel/ui/base/ModelElementHandlerBase.java

...g/fortiss/tooling/kernel/ui/base/PropertySectionBase.java

...oling/kernel/ui/interfaces/IActionContributingEditor.java

...ortiss/tooling/kernel/ui/interfaces/IEditPartFactory.java

.../fortiss/tooling/kernel/ui/interfaces/IEditorBinding.java

...ss/tooling/kernel/ui/interfaces/IModelElementHandler.java

...s/tooling/kernel/ui/services/IEditPartFactoryService.java

...rg/fortiss/tooling/kernel/ui/services/IEditorService.java

...tiss/tooling/kernel/ui/services/IModelElementService.java

...fortiss/tooling/kernel/ui/services/INavigatorService.java

...ortiss/tooling/kernel/ui/services/IPropertiesService.java