added ability to turn off persistence. Waiting on Chris for final changes

This updates the state mixin to be aware of the use_persistence variable

Per Chris's request, this variable is invisible to the user for all blocks where it is disabled. **However** I have left it visible for the StateChange block itself, as it is not disabled by default there. **Please Comment**
I actually did that by accident! I forgot to add it to the stop, haha

Why does it allow you to reset the persistence? Wouldn't it currently just save the persistence of the block that isn't using persistence?

I agree that it would be a good idea to reset (i.e. delete) the persistence if a block isn't using it. Do you want that to happen?