I can do Experiments in Querki

(User Story, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Experiments
Summary: I can go into "Experiment Mode", where all of my changes are stored in-memory and applied only to my current Session, but not persisted.
This is the root story of the Experiments Feature.
That is, during Experiment Mode we intercept all changes -- creations, property modifications, deletions -- in the UserSpaceSession, and hold them there but do not apply them to the Space at large.
This suggests a bit of refactoring of Space to make it work, but I suspect it's not bad. We already have the concept of UserSpaceSession modifications to the Space; this adds to that.
Experiment Mode should be local to this Space, and local to this User.
It must be user-visible: probably a red "Experimenting" label at the top of the page? That would be clickable; clicking on it allows you to commit or discard your experiments.