Add FSM actions to ModelAdmin changelist actions

[blueyed]

It would be useful to have an admin action with changelists to perform transition changes (e.g. soft-deletion) on a list of selected objects (e.g. locks), similar to the submit buttons on the detail view.

This could be handled via ModelAdmin's actions.

The list would contain any possible target transition, or just the valid ones according to the existing/listed objects (from the queryset).
(It might be even possible to only provide valid choices in the dropdown, by using JS and looking at the selected objects, but that's not that trivial then anymore)

I see that this might result in trying to apply invalid transitions, but in this case these could just get skipped (with a message/notification).