Problem/Motivation
The tour module can be automatically started on page load by adding "?tour=1" to the URI. But in a lot of cases you only want to start the tour module once: the first time the user uses this new functionality.
Proposed resolution
Add an extra property to the yml config "show_only_once". This value can be TRUE or FALSE. When FALSE, the tour functionality does what is does in it's current state. When TRUE, the module sets a cookie for this (anonymous) user, indicating the tour has been showed (and completed). Next time when user goes to www.site.com/?tour=1, the tour won't start unless the "tour" button is clicked explicitly.
Remaining tasks
Implement new yml config property
User interface changes
None
API changes
Documentation on how to use this new property
Edit: I'm in the process of creating this patch. But I'm stuck on one thing: how can you update a config entity, without re-installing the module?