Additional API methods for the tabs component

[VizuaaLOG]

Over the next few versions I think it would great to expand the API methods available, allowing certain settings to be changed at run time, rather than needing to recreate the component. The below are ideas for the notification, any other ideas please just comment!

• activeTab(): number - Returns the current index of the active tab
• hoverable(new_state: boolean) - Sets if the tabs change on hover. Returns the current value if no parameter is provided.
• trigger(event_name: string) - This will trigger the provided event on the notification instance. Note: This wouldn't be restricted to documented events, so could be used for handling custom events

New events

• changed - Called when the active tab has changed. Sends the old and new index as parameters

New config

• wrapperClassName - Defaults to tabs-wrapper, sets the wrapping div that this instance should use

The majority of the changes here will also apply to the PanelTabs component that is currently in master. #102