Changes to code editor behavior

Hey, I changed the behavior of your code editor a bit. Here are the things I've changed:
 - Stop if the user modifies the code while running
 - Remove any formatting from the code editor as the user types (useful when somebody pastes from pages with custom formatting)
 - Don't wrap code in the editor: you can now scroll horizontally if your lines are long
 - Allow vertical resizing of the editor to make it easier to deal with longer programs
 - Clearfix on the actions bar
 - `display: block` on the editor div
 - Editor div is a bit taller and with a slightly increased `line-height`

Hope you like it!

**EDIT:** There might be some errors in the way I've handled the Backbone stuff because I've never used Backbone before. Please do feel free to correct me if that's the case :smile: 

**P.S.:** Sorry, I just realized I should have pushed these changes to a new specific branch instead of master. I hope this doesn't cause any problems on your side.