Added tour-<id> class to the bubble element wrapper

a simple implementation as described in #123
Would rather we add this as part of the default template and data passed to the template (see `render()`) instead of attaching the class name as part of `loadTour()`. Class names should be a concern for the bubble to take care of - if we need this as part of the top-level bubble element, `HopscotchBubble` should do this instead. Plus, placing this logic there can allow us to add similar functionality for individual callouts as well.