Notify sync is being paused until connection is resumed by ws

[ZIMkaRU]

This PR adds the ability to send events by WS to notify users when fetching data from bfx_api_v2 is paused due broken internet connection. Available two WS events:

• emitENetError when connection is broken, response example:

{
  "jsonrpc": "2.0",
  "result": "DATA_SYNCER",
  "id": null,
  "action": "emitENetError"
}

• emitENetResumed when connection is resumed, response example:

{
  "jsonrpc": "2.0",
  "result": "DATA_SYNCER",
  "id": null,
  "action": "emitENetResumed"
}

In those two events available the following results, that return caller name:

• DATA_SYNCER - appears when data syncs from api_v2 to DB
• CSV_WRITER - appears when CSV file generates from api_v2
• ACTIVE_POSITIONS_GETTER - appears when UI fetches active positions data from api_v2 for sub-account
• POSITIONS_AUDIT_GETTER - appears when UI fetches positions audit data from api_v2 for sub-account

Depends on this PR:

• Notify sync is being paused until connection is resumed by ws bfx-report#266

[ezewer]

looks good to me!