Staging issue 17 - Dynamic sub-section menus

This pull request to staging branch provides dynamic sub-menu and sub-section menu functionality. 
- Within a given page in the 'default' template, an editor may set two additional variables in the YAML front matter: site_section sub_section
- Templates and includes provide the appropriate right column menu to the page when running "jekyll build" or "jekyll serve" based on template logic that looks at the content of the two variables.
- site_section should be one of the following values, consistent with the top menu items: about, blog, help, download, developers. 
- sub_section may be an array of values in the form [cck,cck-planning] and is used to provide additional level sub-menus. See pages within the CCK or HIG for examples. 
- All menu content is separated into separate include files for updating