gpgsm: New commands --export-secret-key-{p8,raw}

* sm/gpgsm.c: Add new commands.
* sm/minip12.c (build_key_sequence): Add arg mode.
(p12_raw_build): New.
* sm/export.c (export_p12): Add arg rawmode.  Call p12_raw_build.
(gpgsm_p12_export): Ditto.
(print_short_info): Print the keygrip.
artwork: Add 128x128 variant of the logo.

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