Enable access to any generalInfo contents received in PKIHeader

[DDvO]

So far, only sending out a list of CMP_INFOTYPEANDVALUE pairs in the PKIHeader is supported,
but not getting hold of any such pairs received from the server side.
They should be put in a new field of the CMP_CTX and made retrievable via some getter function.

[DDvO]

Also the -geninfo input option of the CLI should be extended to allow more types of input (e.g., strings) and to allow multiple values (separated by comma and/or space).