Restructure and warning cleanup

Now I'm doing a little more serious stuff.

The arch document structure was a little screwy.  It looks like you had a </section> in the wrong place.  It had bumped Security and IANA considerations down to second level headers and made the identity stuff really deep (h5 territory).  I moved this up.

I then fixed indenting throughout (all except the figures).  Then I outdented some of the figures a little.

I then removed the other warnings around unused references by removing the references to the UI security requirements, and the old signaling draft.

This depends on #2.