Close modal window when pushing to backpack, add category subheaders

A few smallish changes:

- The modal window will now close after clicking "Accept to Backpack"
- Category subheaders were added (with programmer layout skillz, so please let me know if it is ugly)
- Categories were rearranged to be ordered:  Peer to Peer, Starter Kit, Connected Educator
- Updated copy on "Accept to Backpack" modal.
- Description field now split into Description and ShortDescription.  An asterisk is used to split the description into these two types of description.
- Starter Kit badge icons will no longer be slightly cut off on the bottom.