Changes for tutorial pages

+ Be able to override sequence labels
+ Be able to define a submenu in data.json
+ Have sub-menus in the primary navigation menus
+ re-do Notices to reflect simpler styling and the need for different
styles (with or without header)
+ FIX: some weirdness with .flag and .body widths. I think this makes
.collapsible less necessary
+ Add all sample tutorial data and content
+ Refine bartender styling

Close #20