refactor the summary group model to fix an issue with leaf groups

change the model to implement a real group hierarchy which can
be cleaned up by pushing up item in leaf groups that are destroyed
Merge branch '1.0' of
ssh://jreimann@gerrit.intra:29418/org.openscada.deploy.git into 1.0

Conflicts:
	org.openscada.deploy.iolist.model.edit/plugin.properties
	org.openscada.deploy.iolist.model.edit/src/org/openscada/deploy/iolist/model/provider/ModelItemProvider.java
	org.openscada.deploy.iolist.model.edit/src/org/openscada/deploy/iolist/model/provider/SummaryGroupItemProvider.java
	org.openscada.deploy.iolist.model/src/org/openscada/deploy/iolist/model/impl/ModelFactoryImpl.java
	org.openscada.deploy.iolist.model/src/org/openscada/deploy/iolist/model/impl/ModelImpl.java
	org.openscada.deploy.iolist.model/src/org/openscada/deploy/iolist/model/impl/SummaryGroupImpl.java
	org.openscada.deploy.iolist.model/src/org/openscada/deploy/iolist/model/util/ModelSwitch.java
	org.openscada.deploy.iolist.model/src/org/openscada/deploy/iolist/model/util/ModelValidator.java