botan: additional openssl dependency

Added OpenSSL dependency, added a Python dependency for the older systems to try and support those a little better, and double quotes everywhere. The download location has also moved upstream. Any attempt to use the old one just gets a redirect to the new one, so I’ve just switched it. For some reason the checksum has changed, but the pgp signature for the download file was verified fine, so *shrug*.
Don't add this unless we know it's needed (i.e. it relies on Python 2.7)