Add a threshold parameter for root cause analysis

[suxi-ms]

Issue

• Users want a threshold to determin whether the selected is a root cause, so we add a new parameter in the interface. The default value is 0.95

[lisahua]

machinelearning/src/Microsoft.ML.TimeSeries/RootCauseAnalyzer.cs

Line 424 in 3cbd97a

return string.Join(";", dic.Select(x => x.Key + "=" + (string)x.Value).ToArray());

When x.Value is long, it throws Unable to cast exception. Probably change to Convert.ToString(..)
private static string GetDicCode(Dictionary<string, Object> dic)
{
return string.Join(";", dic.Select(x => x.Key + "=" + (string)x.Value).ToArray());
}