rate_of_change_test flags are corrupted when the time array is in nano seconds

[leilabbb]

The QARTOD rate_of_change_test expects time in seconds. When the time array uses a different data type the array needs to be tested and a conversion needs to be applied for consistency.

The time data type also affects the threshold calculation in the glider_qc.py. An alternative method is tested to render a more reliable value for the threshold.

This notebook tests the modifications needed for the threshold calculation and applies them to a NetCDF file.

Data annotation will be added to the file to notify users. This is part of the issue #365

[benjwadams]

Nanoseconds aren't accepted by ERDDAP, either. May be an issue because it appears to be valid UDUnits.

[leilabbb]

A draft pull request with a new conditional statement was created to check time units .