tz-aware datetime pd.Series. -> tz information gets lost

[jonasvdd]

When passing a tz-aware non pd.DateTimeIndex (and thus not a pd.Series) to hf_x the .values is performed internally when parsing the hf_data kwargs; which removes the time-zone information; and will display the UTC time.

TODO:

• write tests
• test what happens when we alter hf_data[<ID>]['x'] at runtime with a tz-aware pd.DateTimeIndex