Preview on dashboard

Courses on the dashboard will now show preview screenshots once preview has been run on the course at least once. There are 3 images, mouseover the large image to view them all. 

Also adds a working link to the help button on the add component page, and adds a default case to the help button.
criteria and options vars are not used here - can you remove them for clarity, or add the values that you have passed to the db.update function?