backet \ detection window for pattern analytic unit

[glitch4347]

Only threshold can work without "window": it takes one datapoint from metric and checks if it falls over threshold. In case of pattern and anomaly detector it's impossible to make detection on one datapoint, so we need to define the size of the window which could be used for pattern / anomaly detection. Supposedly, we need to

1. implement method get_detection_window from AnalyticUnit trait.
2. fill bucket in DetectionRunner::run with of size get_detection_window
3. run detection on bucket

[glitch4347]

This task is about pattern analytic unit only, anomaly unit implementation in #84

[glitch4347]

the change should not (obviously) brake threshold detector

[glitch4347]

also this logic on window should work with DETECTION_STEP -- we need update the window periodically. It's a bit not obvious where we should take DETECTION_STEP: from metric service or it should be a new method in AnalyticUnit trait

@rozetko what do you think

(for now we agreed to take DETECTION_STEP from metric_service)

[glitch4347]

I also noticed that in method DetectionRunner::run field t_from and t_to are not updated, so DetectionRunner doesn't work even for thresholds :)