[Active Shooter] real people

So far:

* Replaced Prof Bell with a real person. (the Xav images)
* Removed the outlined hiding person, instead just used Prof Bell (in crouched position) conversation.
* Removed the light switch and doorknob images. Instead just using a transparent rectangle.

Still to come: 

* Add a student to the classroom (they will be the one that runs away).
* Replace shooter.png with our shooter actor (guy who holds the blue toy gun).