Polarion2Capella sync for requirements

[ewuerger]

Sync new non-sync work items back to Capella as Requirements with their link relations
-> requirement text needs to be removed from the generic serializer and moved into its own serializer

Requirements:

• Any Systems Engineering activities take place in Capella (Polarion2Capella only for ReqIF content)
• If the Polarion2Capella sync is used: No ReqIF content is synced from Capella to Polarion anymore (Cycle prevention)