If user has more than one unviewed tour, show them both?

[jabbett]

As we've used Abraham in our software for a while now, we're at the point of adding new features to pages that already have introductory tours. We want new users to learn about all the features, and we want old users to learn about the new features.

Currently, there two ways for that play out:

1. Include the new feature tour content in a second, feature-specific tour. Existing users who have seen the introductory tour only see the new feature-specific one. New users see the intro tour first (without the new feature mentioned) and then have to revisit the same page later to see the second tour.
2. Include the new feature tour content in both the introductory tour AND a second, feature-specific tour. Existing users who have seen the introductory tour only see the new feature-specific one. New users see the same content duplicated in both the introductory tour and when they revisit the same page later, in the second, feature-specific tour.

Neither is a great user experience.

There are a few ways we could improve this:

1. Abraham shows a user all unseen tour content for a page. This approach would benefit from developers writing several smaller tours on a per-callout basis that would naturally string together, rather than large cohesive tours.
2. We add some notion of a "release date" for each tour. Tours with a release date would only get shown if the user had visited the page some time before the release. Of course, this requires Abraham knowing more about the user than just their current_user.id, which may not be desirable or possible in all cases.

Anyhow, open to suggestions!