Refactor and add support for multiple tours and sticky tours.

* Remove changeCookie (isSinglePage remains)
* Add concept of conditions controlling whether tour is loaded.
* Partially separate tour definition and display
* Allow multiple tours in the cookie
* Allow limiting a tour to the first page it was shown on.
* Add PHP unit tests for getting list of tours from the cookie.

Bug: 44924
Change-Id: I9ce5667a55e9f2ad621d0deecfdff6ff12507d96
Merge "Refactor and add support for multiple tours and sticky tours."