Add menuconfig style (and some supporting code).

Notes:
* The shadow used, while not widely supported on every browser, is
  much simpler than the alternative, and if it doesn't work, not
  having a shadow on an older browser is no biggy.
* MenuConfig is a subclass of PackageContainer because of its extra
  text.  The idea is that this interface (or something similar)
  could also be used to configure the kernel on the web.
* All new node creation uses node-creating helper functions; any
  stylistic disagreement can be handled before it creeps into the
  established bits of code, too.
* href's were added to the anchors because not every browser will
  cause the :hover style on a non-href'd A.  The javascript:void(0)
  is the standard "do nothing" href.
* I am trying to keep MenuConfig-specific CSS out of the older CSS,
  although I did remove the debug coloring since it was interfering
  with the fun of menuconfig.