scd: Nitpicks on the improved card prompts

* src/app-openpgp.c (get_prompt_info): Change wording and order
slightly.

The word "Card" was repeated too much in the prompt and moving
signatures to the bottom results in a more consistent layout
between the prompts with signcount and the prompts without.

• Signed-off-by: Andre Heinecke <aheinecke@intevation.de>