Error handling and CLI argument validation

[astronomerritt]

Fixes #85.

• Wrote a class, AdlerCLIArguments, which takes the argparse.Namespace object as input and stores and validates all of the command-line arguments.
• Currently it performs some basic checks to make sure the command-line input is sensible. This can easily be added to as we invent more command-line arguments or come up with more interesting ways the user can provide silly input.
• Wrote unit test and docstrings for the class.
• Rewrote adler.py to fit in with the new code.

Fixes #34.

• If the RSP has not populated a particular field in the table (for example, DP0.3 doesn't have any values for the u or y filter in DIASource/SSSource), we now check for this, populate that dataclass attribute with a NaN, and print a warning to the terminal.
• The original warning has been suppressed because it's not as useful/informative as the one I wrote.
• Docstrings and unit test for additional function I wrote to check if a value has populated.

Minor changes:

• adler.py was failing on the RSP because it was using the old formulation of SSObject. Fixed it.
• I tidied up the constructors on MPCORB, Observations and SSObject to use dictionaries. They're nicer now. This is the kind of thing most people don't care about but I find immensely satisfying.
• The long name for the -s CL argument is now --ssObjectId to fit the rest of the code.
• The attribute Observations.midpointMjdTai is now Observations.midPointMjdTai to match the column heading.

Review Checklist for Source Code Changes

• Does pip install still work?
• Have you written a unit test for any new functions?
• Do all the units tests run successfully?
• Does adler run successfully on a test set of input files/databases?
• Have you used black on the files you have updated to confirm python programming style guide enforcement?

[jrob93]

Hey I just tried this out on the RSP, looks pretty good to me. My only suggestion would be to add a bit more info in adler --help call --filter_list, it just took me a minute to figure out the formatting.

[jrob93]

Also, this is more of a new feature request: should we have a CLI flag for input options other than construct_from_RSP, e.g. construct_from_data_table, construct_from_SQL?