use zones/nameserver IPs/update keys from DB, logging (thanks to asmaps)

remove unneeded stuff from settings
(we still need some in conftest.py for the tests, though)
init DB for tests via conftest.py
more update algorithm choices
give origin zone (if we already know it) to dnstools functions
new views: DomainOverview, DeleteDomain
unify deletion templates using delete_object.html
add django-extensions