Use even newer TourController and animateFromPrev

TourController is an experimental handle for modifying tours
dynamically. Here ArticleCreationHelp has been adapted to
use a newer proposed TourController interface.
See https://gerrit.wikimedia.org/r/#/c/82208/
Also uses a proposed animateFromPrev property
for animating the transition from one step to the next.
See https://gerrit.wikimedia.org/r/#/c/82209/