* Merge from Debian experimental. Remaining changes:
  - debian/patches/xubuntu_improve-nautilus-interactions.patch: added,
    should prevent nautilus from taking over the desktop if xfdesktop is
    running (and vice-versa).
  - debian/patches/xubuntu_fix-duplicate-volumes.patch: fix duplicate
    volumes appearing randomly on the desktop.
  - debian/patches/xubuntu_set-accountsservice-user-bg.patch: update the
    user background property of Accountsservice on backdrop change.
* New upstream release.
* debian/rules:
  - enable all hardening options.
* debian/control:
  - update exo build-dep to 0.7.                              closes: #673730