Accessibility issues with hover controls

[latortuga]

Hi there,

I'd like to request some improvements to improve the accessibility of this library. The controls are not currently usable at all with a screen reader or even just the keyboard. Some suggestions:

• Use buttons instead of divs for things that are buttons (zoom out, zoom in, etc)
• Add focus styling
• Add semantic roles, labels, tabindex, etc to all visible controls as well as all sections of the fully rendered seat map