Enhancement: Add OCM CreateShare to LibreGraph implementation 

- LinkOrShare has been changed to include OCMShares and renamed
- Web app now sends a POST request instead of a GET for OCM invite generation, this has been reflected in the backend.
- Adds the IDP to the user id when returned if user is of type federated.
- Cleaned up dead code since the /sciencemesh/create-share is no longer used.
- Conversions now take OCM shares into account as well.

https://github.com/cs3org/reva/pull/5286/