Bumps covmodel; Adds cal coeff upload utility

Bumps the coverage-model submodule reference to obtain the context management ( 'with …' ) enhancement

Adds ion.util.direct_coverage_utils module - contains the DirectCoverageAccess class which facilitates direct access and editing of coverages.  Preferred use is via context management ( 'with …' ) to ensure proper pausing/resuming of ingestion before and after coverage editing and also ensure coverages are closed properly.

Adds test_upload_calibration_coefficients to ensure the DirectCoverageAccess.upload_calibration_coefficients works as expected.
Merge pull request #1104 from blazetopher/calcoeff_upload

Bumps covmodel; Adds cal coeff upload utility