structure.module

- Addition: made it so that comments can be enabled/disabled on
  a node per node basis, rather then on a category per category
  basis.  The default settings for each individual category can
  be changed though.

  Example: it can be setup so that - by default - all stories
  posted to the category "article" will have comments enabled
  but stories submitted to "announcement" not.

  Different configuration schemes can easily be added later.

  Requires a SQL update, see 2.00-to-x.xx.sql/database.mysql.

- Addition: made submit.php only use categories that users can
  actually submit new content to.