Allow selecting ECC with supported curves when generating new keys

This allows the user to generate ECC keys for smart cards that support
this. They can choose any of the curves supported by the smart card
(and by Kleopatra and GnuPG). This requires the currently unreleased
development version of gpgme.

For current versions of gpgme we at least offer the generation of
Curve25519 ECC keys. Moreover, we remove "RSA 1024" from the available
algorithms. Modern OpenPGP smart cards don't support RSA 1024 anymore
for good reasons (at least according to KEY-ATTR-INFO).

GnuPG-bug-id: 4429