Return fingerprint of first result from import key

This is just a first draft of the capabilities of the import function provided
by GPGME. For now it just returns the fingerprint of the first successfully
imported key.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Enable signatures list in keylist mode

Adding this flag will fill in signatures-related structures when retrieving key
information.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Implement GnuPGKey.getTimestamp

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Remove faulty fclose

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Simple Maven script

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Compatibility with GPGME 1.2.0 (more or less)

Replace some missing features in GPGME < 1.4 with dummy values or by throwing
exceptions.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Ensure compatibility with GPGME 1.2.0

Call gpgme_check_version with the minimal compatible version and redefine some
types missing in GPGME < 1.4.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>