Automatically Self Discover BitcoinZ Wallet Servers

[renuzit]

This issue is to implement a method for self-discovering BitcoinZ Wallet Servers.

New servers should be added to the list.
Missing or non-responsive servers should be removed from the list.

[egyptianbman]

This will probably need to be done in collaboration with BWS in the way that BWS servers ping the seeder when they come to life. We need a way for seeders to ping each other though, to make sure that new BWS instances are realized by all seeders.