Updates zip vs. tar imports (semi fixes #44)

[Korving-F]

This is by no means a full/clean fix for #44 but allows to push in most textual datasets straight from a file (.log / .json) as well as from a zip or tar archive.

Main remaining issues seem to be caused by import errors when things like timestamp fields conflict with the index or other datasets one is trying to push. For example adding two datasets from datasets/atomic/windows/defense_evasion/host/ directory.

{'error': {'type': 'mapper_parsing_exception', 'reason': "failed to parse field [winlog.event_data.TimeCreated] of type [date] in document with id 'bkY71X8B_OeruxpihSOU'. Preview of field's value: '2020-10-21 12:19:04.554'", 'caused_by': {'type': 'illegal_argument_exception', 'reason': 'failed to parse date field [2020-10-21 12:19:04.554] with format [strict_date_optional_time||epoch_millis]', 'caused_by': {'type': 'date_time_parse_exception', 'reason': 'Failed to parse with all enclosed parsers'}}}}

Some successful imports: