Client discovery via multicast

Attampt at implementing discovery of cluster from client via multicast.

Node:
- Added configuration to enable/disable support for client discovery
- Changed MulticastService to work with Object instead of JoinMessage
- Added DiscoveryMulticastListener to handle DiscoveryMessage

Client:
- Added ClientMulticastService
- Added DiscoveryAddressProvider to obtain adresses via DiscoveryMessage

In progress:
- The client must check group name and password to make sure the
DiscoveryMessage is for the correct cluster