Update the lock/readonly icons to use FontAwesome for scaling

I had to update the Closed/ReadOnly icon as there isn't a crossed out chat bubble icon in the FontAwesome arsenal, but I believe the ban circle icon conveys the message...let me know if you'd like me to change it :smiley: 

Zoomed to 200% on Non-Retina
![image](https://f.cloud.github.com/assets/1035315/469869/cd0af51e-b6e2-11e2-9815-f8862edb069d.png)

Zoomed to 150% on Non-Retina
![image](https://f.cloud.github.com/assets/1035315/469842/222c3f9a-b6e2-11e2-8153-ebca3298d944.png)

Normal Non-Retina
![image](https://f.cloud.github.com/assets/1035315/469848/33a399e4-b6e2-11e2-86b0-8b6c013ed767.png)

Fixes #840