Implemented Accessibility Features (Issue #386)

Ended up having some downtime, so I implemented the changes. There are some default bindings at the end, but users can add any binding they want by assigning a keyBindings object in the initialization options. I know you're working on version 4, so if you're ok with this, I can look into porting this sort of functionality over to that version as well (unless you're already adding it in)

Also, since I was in the neighborhood, I switched that media query you had at the bottom of the less source to use a predefined bootstrap variable instead of a hard-coded width (the value of that variable is identical to the value that was there, though)