Include SSG logo into RHEL-6, RHEL-7 & Fedora

These changes are identical to already acked proposals from:
  [1] https://lists.fedorahosted.org/pipermail/scap-security-guide/2014-August/thread.html#5944
  [2] https://lists.fedorahosted.org/pipermail/scap-security-guide/2014-August/thread.html#5945

but since they weren't pushed to master yet, using them to test new GitHub pull mechanism.