DEICH-6403 - Invalid section improvements

If a section/block section is not valid, it gets opened by default, and no sections/block sections with invalid data can be closed. This required changes in ValidationContext (to fire event about sub-context validity) and in DragAndDropItem, to propagate content validity state. Also sections/block sections had to wire up and propaget their validity state to their parent DragAndDropItem instance. Also dumping allValid flag as part og $$_dumpValidationContext(). Fixed issue with sometimes unset validationContext data in $$_dumpValidationContext(). Some layout goodies (using Grid/GridItem in EditPageSectionGeneric)

Closes DEICH-6403