[RCD] pgp encryption

Hello to all, I found many bugs in the gpg encryption module. The only working thing was with a plain mail. Attachments would block the parsing and display of the email.

I modified many points in enigma_engine.php and now everything works as expected (tested with text plain, text plain + attachments, html, html with attachments email). I even added self-signing and private key export, but I don't advise to use them, as they should be further refined. The only thing I did not implement is about signature for non text plain emails (but the signature needs to be removed for non text plain emails to be decrypted correctly).

I would like to contribute my fixes. Can somebody check them, or tell me how to do?

Thanks