Shreds review page. Resolves #22.

 - Implemented a new page that contains current user's tagged shreds
 - Added a pagination macro
 - Moved nav to base.html with a block to extend
 - Next shred loading will only happen on the main page
 - Models now inherit flask-mongoengine's Document in order to obtain
   extended functionality
 - Small CSS fixes
Simplified the prev/next pagination a bit
Improvements for review page

 - Added current user's `recognizable_chars` to the shred item
 - Increased shreds per page to 100
 - Decreased the shred image to 40px for more info space
 - Layout and styling for the shred item
 - Review page now only accessible to authenitcated users
 - Renamed the review page nav item and decreased the brand font size
Merge pull request #44 from dchaplinsky/feature/review_page

Shreds review page. Resolves #22.