It is important that we flush our queued requests
at shutdown and wait until broadcast is completed as a maker need to
remove his offers at shutdown.

- Add handling for the case that there are very few connections (as in
dev setup).

- Make BundleOfEnvelopes extend BroadcastMessage

- Add complete handler for broadCaster to shutdown in P2PService and
wait with shutdown of other services until broadcaster is completed.
- Remove case for repeated shutdown call on P2PService as it cannot
happen.

# Conflicts:
#	p2p/src/main/java/bisq/network/p2p/P2PService.java

…ndle-msg-at-broadcast

# Conflicts:
#	p2p/src/main/java/bisq/network/p2p/P2PService.java

# Conflicts:
#	p2p/src/main/java/bisq/network/p2p/P2PService.java

…ndle-msg-at-broadcast

I don't know why the tests failed as I just added an overloaded method
and it should not have any impact. There is also one exception which
makes it even more obscure. I guess its some test framework issue.

See comment at the exceptional handling
// If we remove the last argument (isNull()) tests fail. No idea why as the broadcast method has an
/ overloaded method with nullable listener. Seems a testframework issue as it should not matter if the
// method with listener is called with null argument or the other method with no listener. We removed the
// null value from all other calls but here we can't as it breaks the test.