Add data attribute to the body for the currently active tour name and current step

[BrianSipple]

Following up on the discussion here

[BrianSipple]

@rwwagner90 @chuckcarpenter Since tours currently don't have a name or id property, I'm curious about your thoughts regarding how exactly we could design this.

One approach would be to allow for a name option to be passed to the Tour constructor, and then have the constructor set it as an instance property. If name isn't passed, Shepherd could generate a unique identifier for the Tour and use that.

From there, Tour._setupActiveTour could do something like this:

    document.body.setAttribute('data-shepherd-active-tour', this._name);

[RobbieTheWagner]

@BrianSipple I believe that is how id was supposed to work, but as Chuck noticed, it was always undefined. Perhaps we were not passing the right params to get it set, but I think your approach sounds good.