Profile privacy feature

https://www.pivotaltracker.com/s/projects/982890 
https://www.pivotaltracker.com/s/projects/982890/stories/64970358
https://www.pivotaltracker.com/s/projects/982890/stories/65424974

- fix for back button (legacy URL issue plus bug open by Pavel)
- per Thomas fixed the carot on sidebar from upward to right facing position.
- added ul, li and target to html whitelist in documents_helper.rb
- added public/private profile feature
- added controllers specs and cukes scenario to test private profile is hidden
- implemented pending steps in users_controllers_spec.rb file