Document revisions

Changes the "Revisions" button behavior in documents. Allows to show/hide the number of revisions made on the currently opened doc. 
PT Story: https://www.pivotaltracker.com/story/show/72539552
Heroku Instance: http://damp-lowlands-2351.herokuapp.com/projects/et-omnis-aut/documents/quis-nulla-ipsam