Handle ActiveRecord::RecordNotFound with 404 Page

- Use find_by! to throw exception
- Add rescue_from ActiveRecord::RecordNotFound in ApplicationController
- Re-do 404 page to show content inside application layout
UI Fixes

- Add user Glyphicons
- Move login/logout to right of navbar
- Align Glyphicons icons to text baseline
- Update URLs
- Renamed to Hushed Tones