card: Make printing of key information more flexible.

* tools/card-tool-misc.c: New.
* tools/card-tool.h: Rewored data structures for key infos.
* tools/gpg-card-tool.c: Ditto.
* tools/card-call-scd.c: Ditto.

Note that this also changes the way the key information is printed.
Formerly we printed it like:

Signature key ....: <openpgp-fingerprint>
      created ....: <timestamp>
      keygrip ... : <keygrip>

now we do:

Signature key ....: <keygrip>
      fingerprint : <openpgp-fingerprint>
      created ....: <timestamp>

This is because a keygrip is always available but a fingerprint and
the creation date are properties of an OpenPGP card. A standard way
of listing keys is better than one depending on the type of card.

• Signed-off-by: Werner Koch <wk@gnupg.org>