Add mechanism to inject fake keyword values

It would be useful to be able to create/inject MHS keywords just as if they had been added by some actor. There are a couple of plausible ways to do this: in the tron hub, since it is in a position to lie about anything, or in the actor itself, probably by adding a tron_actorcore command. I actually have the first, just not enabled, and the second would be trivial to add.

Not sure which. Maybe both: using the actor is less fake and tests more but also requires the actor to be running, which might not always be the case.