Feature/apl 2220 nagios rest api

[yuriy-ln]

Updated code and logic

• added node 'isDownloading' field and logic, we don't consider it for 'max diff' evaluation
• added 'isLive' node's field, so we don't consider it in logic
• added REST API method for getting OK / WARN / CRITICAL test net status
• updated logic for storing 'history max diff' values
• updated logic for finding 'mutual block' between nodes
• refactored code for fetching Node's data, extracted to separate component
• added config HM parameters