Keyboard shortcuts Customization
Right off the bat, your code needs some serious indentation. It's barely readable given its current state. If you happen to use Sublime Text, there's HTML-CSS-JS Prettify plugin.

Another thing I noticed is you're loading jQuery twice.

Next, your code is highly coupled. Your condition to check the buttons are highly coupled to the behavior it does. What would happen if I want to change the behavior to another key? Or what if you want to operate in another platform which uses different keyboard norms (Mac vs PC)? You can read Game Programming Patterns to get an idea of configurable keys.

Another thing to consider is what if the user wants to bail out of a level? What if the user accidentally pressed a button that progressed him a level, but wants to go back and use another combination instead? Usually Esc was reserved for this. For multi-press button combinations, releasing all buttons is an option.

jQuery also has event.which which is a normalized version of charCode and keyCode.

Your code lives in the global space, which means level is highly modifiable and pollutes the global namespace. You could put your code inside a closure, an IIFE to be exact, to prevent that.