Update OpenSSL logos

Add two new files

  doc/images/openssl-square.svg
  doc/images/openssl-square-nontransparent.png

and update the existing file

  doc/images/openssl.svg

The "square" versions of the logo write "Open" and "SSL" on separate
lines, so that less horizontal space is used.

The png file (nontransparent, white background) can be used to update
the profile picture for the OpenSSL organization on GitHub.

For the existing logo, openssl.svg, the subtitle "Cryptography and
SSL/TLS Toolkit" has been dropped and the text-elements have been
converted to paths (so they are no longer dependent on what fonts the
renderer provides).

The svg files were provided by Anton A.

Part of openssl/project#262

Reviewed-by: Anton Arapov <anton@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from #22626)

(cherry picked from commit 339e5cb)