Allow User to adjust editor font size

Leaves 14px as default, but adds the option to change font size.

![image](https://f.cloud.github.com/assets/4098889/355138/72c6b2ac-a0c9-11e2-9249-faf446540ce5.png)
![image](https://f.cloud.github.com/assets/4098889/355140/a4c41470-a0c9-11e2-8846-3f62e3aad2bf.png)