user/xmlsec: fix tests, add -gcrypt and -gnutls, and more

• URL changed to official website.
• Source changed to official download URL instead of GitHub archive.
• Tests were being skipped spuriously due to the test suite being broken. The relevant commits to fix this have been backported and applied.
• Add the -gnutls (for experimental/aqbanking) and -gcrypt (required in order to build -gnutls) subpackages.
• The *.la files have been removed from the main package (remove options=libtool). It is assumed these are no longer needed, since the only official reverse dependency at this time is libreoffice, which uses pkg-config and not libtool.
• usr/lib/libxmlsec1-nss.so was moved to -dev by running the -dev split function before the plugin split functions.
• usr/lib/xmlsec1Conf.sh was moved to -dev.