[debian] qcluster causes a high database load

Hi,

Followup from a debian bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914099

HyperKitty should use a default queue polling higher than 0.2 which is the default set by django-q (https://django-q.readthedocs.io/en/latest/configure.html#poll)

Something like 5 seconds would look fine I guess?

Cheers!