ts_list to dataframe

[khider]

Need a new functionality that transforms the legacy ts_list (from get_timeseries) into a data frame whose columns corresponds to the entries in the various dictionaries contained in the list.

Although this wouldn't replace a good querying function, it will enable users more familiar with pandas to work with the data directly.

@nickmckay Is this how LipdR works now?

[khider]

Instead of creating a new function, add a parameter dataframe=True to return the data frame along the list.

[khider]

done in 5907fa9a360d2d907216dd302a49e902be60c027