Refactor lightbox component

[jameshopkins]

Aims

• Give the author full control of when lightbox instances can be interacted with - i.e not just implicitly bound to .click()
• Remove jQuery dependency
• Expose Lightbox constructor so the user can inherit the object and create their own site-specific lightbox instances

Would be a good excuse to fix #295 and #298, too

[jameshopkins]

The lightbox component I've created can be seen at https://github.com/jameshopkins/lightbox. A few things to mention that are different to the current implementation, namely to do with separation of concerns:

• hashManager integration lives outside the core component, and instead, instantiation is controlled through the attach event. open and close events can be used to populate history.
• Element focus control lives outside of the core component
• AJAX content loading isn't currently supported, although theoretically, it should be fairly easy.

We'll be using it in the coming week, so will be able to iron out any issues.