card: Implement the bulk of OpenPGP stuff into gpg-card-tool.

* tools/card-call-scd.c: New.
* tools/card-tool.h: new.
* tools/gpg-card-tool.c: Largely extended.

gpg-card-tool will eventually replace the --card-edit command of gpg
because it makes more sense to have a multi-protocol aware tool and
not just one for OpenPGP cards. Most OpenPGP card things works now
but a few, those which require close interaction with gpg, still need
to be implemented. And of course the whole planned non-interactive
stuff needs to be written.

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