Implements direct editing of SPointingRelations
Almost fixes the refresh problem on deletion of Edges, TODO: introduce
proper switching in Adapters

- Use removeNotify() in RelationAdapters when getNotifier() =
getModel(), oldValue = SDocGraph, newValue = null!

- Introduce switching & triple checking & perhaps further checks to make
sure children can be refreshed

- Throws IllegalArgumentException in some cases (solutions above)
Improves refresh of connection parents

- implements proper switch statements in Adapters

- adds eNotifys to source and target of connections
Implements edit policies & commands for annotation and deletion for
SDominanceRelation
Struggles with removal of single SStructure
Unfixed bugs
Implements direct editing for edges, fixes refresh bug on creation and
deletion of elements
Prepares direct editing on creation of connections