[TCP] Change client side peer dicovery according to TCP update.

[Aminion]

Implement Bitcoin-like discovery. Auto-mode:

• Try to fetch peers via DNS lookup.
• If lookup failed or less than 2 peers provided, use embedded in executable list of peers
• continuously keep amount of connected peers against 16, not less than 2

Manual mode:

• wallet strictly rely only on list of indexers, provided by user

Network page re-implementation description:

• single list, containing all known peers
• ability to add and delete custom peers (marked with star)
• ability to exclude peer from usage by system
• list sorting - 1 connected custom peers; 2 disconnected/suspended custom peers; 3 connected discovered peers; 4 disconnected/suspended discovery peers;

[NCrashed]

https://github.com/sipa/bitcoin-seeder

[NCrashed]

Related #678