function bindOverlayKeys(state, content, dismissable){
    overlayHandlerContent = content
    document.removeEventListener('keydown', overlayKeyHandler)
    document.removeEventListener('keydown', overlayKeyDismissableHandler)
    if(state){
        if(dismissable){
            document.addEventListener('keydown', overlayKeyDismissableHandler)
        } else {
            document.addEventListener('keydown', overlayKeyHandler)
        }
    }
}
Bind overlay keydown listeners for escape and exit.

@param {boolean} state Whether or not to add new event listeners.
@param {string} content The overlay content which will be shown.
@param {boolean} dismissable Whether or not the overlay is dismissable