Overwrite the getIncoming/getOutgoing EOps of PlatformConnectorUnits
These eOps are not overwritten, thus returning IConnections. Instead, TransmissionConnections should be returned that are the only allowed connections for this connector type (AFAIK).
Overwrite the getters/setters with return a casted list to ease programming againts these models.
(from redmine: issue id 3722, created on 2019-04-26)