Draconian control of nginx config files

Changed the nginx configuration & sites-enabled mechanisms to look for unmanaged files and delete them.
Less draconian total control

Harsh management now opt-in.
Remove unwanted defaults; fix config-check mistake

We should always check the nginx configuration, not just when the 'keep_only_specified' flag is turned on.

Also, if it isn't, we should try to clean up the default nginx packages a bit.
Merge pull request #12 from sethp-jive/master

Draconian control of nginx config files