NOTES.change_PR13

Change description and rationale
--------------------------------

This PR improves the handling of missing ACE data and adds infrastructure to test various
missing data scenarios.

- Instead of dropping bad ACE data at the point of reading in values, leave the bad values
  there (as indicated by a negative value) and do downstream handling of bad values.

- Indicate bad or N/A values with bold red text in the state table. If there is no average
  P3 from MTA then use 0.0 for fluence prediction but show fluence as red.

- Plot bad ACE values so viewer can more easily see missing data. This shows up as a
  vertical line to the bottom of the plot.

Code changes (list affected files and provide code diffs)
---------------------------------------------------------

See: https://github.com/sot/arc/pull/13/files

Testing
-------

Used unit tests to simulate various data loss scenarios and confirm
desired behavior.  Ran code in the development environment for several
months and saw no unexpected outputs in run logs.  Saw expected
improvements during periods of actual ACE data loss (see attached figure).

Interface impacts
-----------------

No change in interface.

Review
------

Community was notified about development version.  No external code review.


Deployment plan
---------------

Will be deployed as soon as approved due to current ACE data loss event.