aqbanking: 5.6.12 -> 5.7.8

Upstream changes in 5.7.8:

  * Update bank information files for German banks because the format of
    ZKA files has changed in the meantime.

Upstream release notes in German:

https://www.aquamaniac.de/sites/download/releasenote.php?package=03&release=217

Upstream changes in 5.7.7:

  * Fix of manually adding new HBCI accounts (for example using
    KMyMoney).
  * Fix wrong truncation of account numbers in some turnovers of the
    SWIFT parser.
  * Simplified code for inserting new account data while fetching HBCI
    accounts.
  * Update information for German banks.

Upstream release notes in German:

https://www.aquamaniac.de/sites/download/releasenote.php?package=03&release=216



As with the gwenhywfar update, the updater script (update.sh) actually
didn't get the right file to download, so I temporarily modified it to
download file number 2 because file number 1 is the GPG signature. The
reason why I didn't fix the updater is because the upstream site will
have different URLs in the next upcoming version, so our updater is
basically end-of-life for now.

I also changed the package expression to use the version from
sources.nix instead of a hardcoded value.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @goibhniu