Redvox

* Added a property: tri_message_coeffs to `redvox/api900/timesync/api900_timesync.py` to allow access to the tri-message coefficients
* Allowed access to the function evaluate_latencies_and_offsets in `redvox/api900/timesync/api900_timesync.py`

* Added unit tests for `redvox/common/stats_helper.py`
* The functions mean_of_means, variance_of_means and mean_of_variance in `redvox/common/stats_helper.py` will not fail when sum(counts) is 0.

* Added validation function that removes duplicated timestamps to `redvox/api900/timesync/tri_message_stats.py`
* Added get_latency_mean, get_latency_std_dev, get_offset_mean and get_offset_std_dev functions to `redvox/api900/timesync/api900_timesync.py`
* Updated unit tests

* Expose new package `redvox/api900/qa`
* Expose new gap detection module `redvox/api900/qa/gap_detection.py`
* Provide a public identify_time_gaps method

* Add and define useful constants to `redvox/common/constants.py`
* Add cross-correlation functions to `redvox/common/cross_stats.py`
* Add date time utilities to `redvox/common/date_time_utils.py`
* Add rdvxz file statistics functions to `redvox/common/file_statistics.py`
* Add statistical helper functions to `redvox/common/stats_helper.py`
* Add new time synchronization package at `redvox/api900/timesync`
* Add a location analyzer to `redvox/api900/location_analyzer.py`
* Updated unit tests and documentation
* Updated dependencies to latest versions
* Added additional code QA (pylint, mypy, coverage)

* Update bulk data download client to utilize a RedVox provided authentication token