Feature: Ability to specify random destination node in graph from config

[carlaKC]

Allow destination in config to be * and interpret it as a new / random node in the graph on each payment, so that the simulator will fire off payments to arbitrary locations.

[carlaKC]

Now that we have random activity, I think that there's less of a use case for random destinations in described activity.

Closing for now, we can re-open if this is something folks want.