staging merge into master

[Maxim Cournoyer]

Hello,

I'm planning to merge staging into master soon (tomorrow or friday),
unless someone has a problem with it.  It includes at least two CVE
fixes as well as a bunch of updates such as a newer gstreamer, ffmpeg,
qt 5, python-cryptography and a few others, and seems to be close to
master in terms of coverage (currently 68% for staging vs 73% for
master, according to https://ci.guix.gnu.org/).

I was able to reconfigure my system with it, and haven't seen issues so
far.  Testing welcome!

-- 
Thanks,
Maxim