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Improvements
- More helper functions (``get_local_timezone``, ``timestamp_utc``, ``timestamp_utc``) are created.
- ``initial_bundle_data`` method is now available in Base Elasticsearch engine class,
meaning that it is possible construct Bundle initial data into the derived class, so more flexibility.
Bugfixes
- Default bundle initial data was constructed ``meta.lastUpdated`` value with utc now time but without timezone offset, so
during json serialization, timezone info was missed as a result reverse construct of Bundle complains validation error.