clean up default phpTemplates

In anticipation of a new core theme, we need to start cleaning up markup in various places. This patch cleans up all of the default tpl files. Fixes some semantics and improves the spacing and readability. The latter is very important--while teaching new people how to theme in Drupal, this was a big complaint. When it was spaced properly they understood things better.

Although this looks like a lot is added/deleted, very little it. It's mostly a spacing/formatting patch, with a couple useful classes and few extra sematics elements used.