[guesser] Datetime guesser

This uses dateinfer to guess at a datetime format that could be used to parse an array of strings as datetimes. It then tries it out and returns the percentage that worked.

Future enhancements:
    - determine if it's a list of seconds or milliseconds since the unix epoch as well
    - if the data is messy (eg some dates are in one format, others are in another format) how to split up the data and deal with that.