Implement stateful requester for gossip

[jonastheis]

From here:

the ticker API is bad, where the interaction happens via the Tick event. Thus, you always hook to that event. I think it would be much better design (don't need to do it now) to make the ticker receive a function with the type that gets executed on each tick.

The EventTicker should be changed accordingly.

[alexsporn]

Tbh I would move away from the event ticker altogether and implement a stateful requester between the network layer and the protocol for #591 that tracks what is being requested, from which peer something was received etc. That is the way we did it in HORNET to avoid flooding neighbours with stuff they already sent to us, etc., and to properly track when stuff was requested, pending, received, etc.