- Vcard chunks may be received through the IncomingMessage and
  IncomingAccountMessage signals. This patch implements handling
  of the latter.

- This patch also handles cases where a vcard has only one chunk,
  and where the photo is empty.

Change-Id: Id0e9a5c74284e85be729c972a16a14ebb0a9dd24
Tuleap: #1436