BL-780 Refine which PDF controls show in Publish view

* Hides "Show Thumbnails" button, which didn't do anything
* Hides sidebar with thumbs
* Enables "Toggle Sidebar" button, which now works to show
   the thumbs when clicked.
Merge pull request #170 from gmartin7/BL-780MorePdfControlWork

BL-780 Refine which PDF controls show in Publish view