Add a separate default detector & fix threshold range for ema detector

1. currently when bitmap detector throws an exception due to lack of data points, exponential moving average(ema) detector acts as the default detector. Adds a default detector which uses both ema detector and derivative detector.
2. The 10% default threshold is too low for ema detector. Change score method and use a different threshold.

We decided to use <1, but after running with couple examples I found 0.1 gives better result, since in some cases, ~0.8 are data values we don't want to ignore.