some code cleanup
Added interfaces for activities.
Removed setter from properties
Created Linq Queries for filtering the nodes and edges of an activity from the ownedItems
activity interfaces added to diagram
results of activity-stuff review
Corrected spelling of ExpErrorOnPrpopertyInitOfUmlObject to ExpErrorOnPropertyInitOfUmlObject

Added ActionTypes for all Action-MetaTypes in EA

Implemented lazy loading for Activity Property of ActivityEdge and ActivityNode

Implemented Linq query for filtering the incoming and outgoing edges of an ActivityNode
Willert requirements implemented
Willert requirements implemented
Willert requirements implemented