base.css: don't style `#footer-nav` directly

We currently have invalid markup: two elements with id=footer-nav.  This
change means that the footer-nav ID is unimportant, so we will then be
able to remove it from both of the elements that bear it.
Remove "footer-nav" IDs
Delete excess double-quote in authorpic sidebar

Fixes #190.

I don't know who fixed this in the database templates; I'm merely
committing it to the Git repo.