Optimize _detect_window_size within DataExploration for weekly data

[sayanchk]

_detect_window_size is currently not optimized for weekly time series data in order to detect the most frequent periodic pattern. This issue need some investigation on that front. Reference: https://github.com/zillow/luminaire/pull/114

Note: This method is a dependency for Structural, Filtering and Window based models. Therefore, any change in this method requires testing on any existing supported (or rather optimized on) time series data types (daily, hourly and even higher frequencies). Please refer to the datasets for testing.