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

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;