Allow empty <h2> first.

Allow empty <h2> first.

 - In the database, contents.sectionname is no longer 'not null'.
 - Edit script has been changed to allow first section name to be
   empty (setting contents.sectionname to null).  Only for the
   first section, however.
 - Create script now creates an empty first sectionname by default.
 - Page has been changed to render empty sectionnames properly (no
   <h2> title or anchor).