Security fixes
Upgrade Tor Browser to 7.5.4 (MFSA 2018-12, Closes: #15588).
Upgrade OpenSSL to 1.1.0f-3+deb9u2 (DSA-4157).
Upgrade Perl to 5.24.1-3+deb9u3 (DSA-4172).
Upgrade Libre Office to 1:5.2.7-1+deb9u4 (DSA-4178).
Upgrade libmad to 0.15.1b-8+deb9u1 (DSA-4192).
Bugfixes
Enable the removal of OpenPGP keyblock in Whisperback (closes: #7797).
Show the logo in Whisperback's About menu (closes: #13198).
Use the same font in all the Whisperback report (Closes: #11272).
Update zerotracepen-bugs@zerotracepen.boum OpenPGP key (Closes: #15534).
Minor improvements
Stop installing python-qt4 and python-trezor (Closes: #15391).
Make WhisperBack easier to find in the GNOME Overview (Closes: #13299).