Starshade updates

[maxwell-zweig]

Describe your changes

Added two classes (OrbitVariationaFirstOrder.py, OrbitVariationalDataSecondOrder.py) to the Util file in EXOSIMS to compute STMs and STTs for calculating delta-v costs.

Added KulikStarshade.py into the Observatory folder, and modified Observatory L2 Halo to include an option "use_alt" to use with KulikStarshade.

Added an end-to-end test for KulikStarshade.py in the Scripts folder, also added a new scheduler class kulikJScheduler.py for use with KulikStarshade, which provides similar functionality to occulterJScheduler but is for use with KulikStarshade since occulterJScheduler is for use mainly with SotoStarshade.

Added some test cases for KulikStarshade in tests/Observatory

Type of change

• New feature (non-breaking change which adds functionality)

Reference any relevant issues (don't forget the #)

Checklist before requesting a review

• I have verified that all unit tests pass in a clean virtual environment and added new unit tests, as needed
• I have run e2eTests and added new test scripts, as needed
• I have verified that all docstrings are properly formatted and added new documentation, as needed

[dsavransky]

starshade_synch branch cloned to origin repo for further development and cleanup of merge conflicts.