backend:
* enhance the whitelist function. Now sub-domains could be whitelisted
  (e.g. 'fakenews.facebook.com'), even if the correspondent tld is
  blacklisted (e.g. 'facebook.com') - this makes whitelisting
  much more flexible and predictable
* rework the domain query function to adapt the whitelist changes
* refine startup error checks/messages
* small fixes

luci:
* cosmetics

Signed-off-by: Dirk Brenken <dev@brenken.org>