Revert "Remove DNS build tests (they'll be fixed later)"

This reverts commit dd00a9b65be2cf44b6b2c6bff0ac91dadb386ea1.
It's something
Add a build test fixture
Add some tests
"Finish" DNS build tests; fix some broken things
Do verbosity in dhcp_build too
Change DNS build test fixture name
Don't try to add files when empty=True
Write a DHCP build test
Fix some verbosity and directory name issues
Remove unused module
Add extra files for testing

(Our build process requires them.)
Enable AJAX submission for network forms
Enable AJAX form submission for range and vrf
Enable AJAX for every form except the system one
Fix DNS AJAX form submission
Get up to date
Merge branch 'master' into build_tests
PTRs render records correctly
dynamic ranges build reverse correctly