Test cases for IMS eCall and MCPTT have been requested by RAN5, which require updates to LibSip and MIME body type definitions by 3GPP TF160

---------------------------------------------------

New eCall TCs require an update of MIME type defs :
- Container for MSD data
- MIME field Content-ID
See R5-174537 based on main eCall RFC 8847

---------------------------------------------------

MCPTT default message contents in R5-173766 (TS 36579-1 v.0.2.0) require following new headers:
- Answer-Mode RFC 5373
- Priv-Answer-Mode RFC 5373
- Resource-Priority RFC 4412
- Target-Dialog RFC 4538
- P-Answer-State RFC 4964

-------------------------------------
          - import statements changed to avoid circular imports
            - import of LibSip_Common
            - types of LibSip_Common are commented out (Charstring_List, GenValue, GenericParam, SemicolonParam_List, AmpersandParam_List, CommaParam_List)
          - import statements changed to avoid dependency of PIXITs
            - import of LibSip_PIXITS commented out
            - c_mimeMultipart commented out
          - definition of DisplayName added
          - NameAddr changed to use DisplayName instead charstring (acc. to R5w140111)
          - featureCaps restored in MessageHeader
          - encoding rule "SIPCodec" added to types Request, *_Request, RequestUnion, Response (note: how to deal with this in the future is FFS)