captureContent parameter in NewHar() method to capture body content of HTTP requests.

[masoudk1990]

• Added an optional parameter in NewHar() method to capture body content of HTTP requests.

/// <summary>
/// 
/// </summary>
/// <param name="reference"></param>
/// <param name="captureContent">Whether to capture body content of requests or not</param>
public void NewHar(string reference = null, bool captureContent = false)
{
    MakeRequest(String.Format("{0}/{1}/har" + (captureContent ? "?captureContent=true" : ""), _baseUrlProxy, _port), "PUT", reference);
}

• When starting the server, if it fails it displays a proper detailed error message.

throw new Exception($"Can not connect to BrowserMob Proxy - {_errorMessage}");