trigger-state node :: check flow/global variables.

[code-in-progress]

It would be nice if the trigger-state node could include flow/global variables as part of the conditions. Currently under Conditions, we have a choice of "this entity" and "entity id". It would be really flexible if we could also have "flow variable" and "global variable". That way, one could further filter on when the node fires.

For my use case, I set a flow variable named "notification_fired". I currently have to test for that right after an entity triggers the trigger-state node using either a function or a switch node. I could reduce that into one node by having a condition that checked if that flow|global variable was set (and/or set to a value) inside of the trigger node.