Multi_ts data type
Added new data type - multi_ts. It can be used for training models not only on one time series (lagged matrix of one ts), but on the number of time series with the same variable. The main difference from multimodal data is the specialty of lagged matrix building. For multi_ts tagged transformed tables for each time series stacks verticaly and use as target the same time series, not the main one. This allows to expand the training sample.