Use similar S/MIME icons as Outlook
* forms/Makefile.am: Add new files. * encr-s-smime.ico, encr-s-yellow.xcf, ribbon-red.xcf, sign-s-smime.ico, gpgol-form-signed-smime.cfg, gpgol-form-signed-smime-opaque.cfg, gpgol-form-encrypted-smime.cfg: New.
This introduces the Message Class
"IPM.Note.GpgOL.SM.MultipartSigned" to display a similar ribbon
as Outlook does and for better distinction internally.