This PR prevents proxying all HTML of the bfx api error

In some cases, the bfx api may respond just HTML instead of expected json in the raw body https://github.com/bitfinexcom/bfx-api-node-rest/blame/master/lib/rest2.js#L166
For example: maintenance mode, nginx 502 Bad Gateway error, 403 Forbidden for the staging server, check the screenshot:

The idea is:

• don't proxy all HTML
• extract a string of the title tag to use as a description of the error
• and pass it to the corresponding field of an error

Basic changes:

• Prevents proxying all HTML of bfx api error
• Adds forbidden resource error tester
• Handles forbidden resource error
• Adds test cases for response service for handling error with html and plain text in the response body

Request example:

{
  "auth": {
    "apiKey": "api_key",
    "apiSecret": "api_secret"
  },
  "method": "verifyUser"
}

Response example:

{
  "jsonrpc": "2.0",
  "error": {
    "code": 403,
    "message": "Forbidden",
    "data": {
      "bfxApiErrorMessage": {
        "bfxApiStatus": 403,
        "bfxApiStatusText": "Forbidden",
        "bfxApiRawBodyCode": "Code is not abailable",
        "isBfxApiRawBodyResponseHtml": "Yes",
        "bfxApiRawBodyResponse": "Access denied | api.staging.bitfinex.com used Cloudflare to restrict access"
      }
    }
  },
  "id": null
}

Error logging examples: