143 Adding JSON constructor methods.

[astronomerritt]

Fixes #143.

• There is now a constructor, AdlerPlanetoid.construct_from_JSON(), which allows you to construct the AdlerPlanetoid object from a JSON file. This is so we can create the object from a Kafka alert.
• Note that it assumes there is only a single value for each JSON key, i.e. that none of them will be lists.
• Also note that this has not been unit tested.

Describe your changes.

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?