Merge 7-node-module

[originalmk]

This PR adds node module, which provides mainly Node and NodeStore abstractions:

• The NodeStore is an actor and communication with it is based on messages and allows to store or load Node-s from disk.
• The Node is just a set of data related to running a swarm, its data will be saved in multiple files on the disk.
• The NodeConfig is a struct containing node configuration loaded from JSON file.