shepherd.js tour for data layers panel

[patudom]

BEST AQI educators were very enthusiastic about idea of conditional tour where user can't progress to the next thing until they have completed a required action, like making a region, etc.

They also liked the idea of including some "hooray you've finished" indicator that they can screenshot to demonstrate to teacher that they completed the activity.

[Carifio24]

@patudom Just wanted to say that cosmicds/vue-toolkit#118 has an implementation of preventing advancing to the next step until a condition is met, feel free to borrow that implementation if it's helpful

[patudom]

Notes from #250 so everything is in 1 place:

Let the tour be step by step, where users cannot advance to the next step until a condition is met (like there are now >0 region cards).
(To avoid the situation I had with the tour where it crashed when there was a step that wanted to attach to an element that didn't exist in some states: according to our quick web search, there is a way to pass a promise that you expect to resolve before the tour step is shown. If you create an element during that promise it won't try to attach itself until after the promise is resolved.)

[patudom]

From workshop suggestions:

• Demo clear labeling of regions/time ranges/datasets.
• Make clear that user can change opacity of regions or hide them from being displayed