Emit signals for when the dock is triggered to show or hide.

Hi Michele,

Here's the pull request to emit signals for when the dock is triggered to show or hide.

Sorry for the delay, but I needed to do some testing to make sure things worked properly. BTW, I avoided placing the emit signals within the _animateIn & _animateOut functions because they are called directly from other functions like disableAutoHide, resetPosition, pageChanged, onAccessibilityFocus, etc).