Service client behaviour

[stonier]

A common pattern is to shoot off a service request. Probably need to handle:

• Type
• Service Name
• Request (either pass in the constructor or point to a blackboard variable)
• Functional callback for the response (pass in the constructor)

[stonier]

Needs to be non-blocking so as not to blow up the tree. So ... drop into running while it's waiting for it's future and then have a callback handler for the response to flip it to success / failure on future ticks.