Make nginx more convenient; clean up caveats

No shin, screw that. Make nginx use a sensible docroot. All web servers should use this docroot from now on. I suggest the symlink method to making them do this so it is easy for people to change this on a server-by-server basis and have multiple docroots.
libwebsockets: use git checkout

Rationale: the tarballs are timestamped so the hash changes on every
download.