User show view and dashboard refinements

Some various adjustments to the user show view and dashboard. Changes
include:

- Add media queries for dashboard and users show view.
- Start to conform users.scss and dashboard.scss to SCSS style guide.
- Improve no data messages on profile.
- Display chef icon next to chef username.
- Display linked GitHub accounts on profile.
Merge pull request #382 from opscode/user-dashboard-fixes

User view and dashboard view fixes