Production of Discovery branch changes as separate deliveries.

[Aminion]

To overcome complexity of merging, developing and reviewing, changes need to be split. Each change goes as separate task, separate branch and pull request. Discovery related changes and collateral refactoring should be extracted from branch and split to:

• package containing all constants, shared between both client and nodes (DNS, seeds, inital nodes)
• moving and unification of functions related to transformation of Address, SockAddr, Text addrs to above described package
• fetching initial nodes via DNS lookup for both client and node
• late DNS resolving for node addresses on client
• network management based on single Set of known nodes, with single tab in settings
• automatic discovery mode switch control and background worker