Add better explanations and output for rb-site and Manual Updates.

rb-site and the Manual Updates pages didn't go into the <Location> field
changes that were needed, which ended up confusing users. These are now
covered, as are equivalent lighttpd changes.

The rb-site resolve-check command was also a little confusing in that a
second resolve would say that there's no known check. Now it says that
the check was already resolved.

There's also a few style fixes so the manual update page is more
readable in general, and particularly when the stylesheet can't be
loaded.

Tested creating and upgrading sites, and verifying the information within.

Tested the manual updates page with and without stylesheets.