Download products from event subscription JSON files

[snbianco]

Main Objectives:

• Enhance MastMissions.download_products to accept JSON data from the upcoming MAST subscription service (either as a local JSON file or an in-memory object).
• Add full MastMissions support for IUE to streamline workflow.

Other Notes:

• More robust error handling when a user tries to input a filename to MastMissions.download_file when the mission requires a URI. Unfortunately, I don't know of an easy way to tell which missions require this from the API, so the list is hard-coded (for now).
• MastMissions.download_products looks for dataset or fileset keyword when creating the download path for files. If neither are found, instructs user to use flat=True.
• Finally got around to making some changes to mast_test.py that simplify mocking and making calls to functions. It looks like a lot of changes, but really, I'm just removing the prepended mast. from everywhere it was used.
• We recently had a change to one of our services that was evoking a warning in tests that query the PS1 catalog in test_mast_remote.py. I avoid these warnings by selecting certain columns in the tests.

[bsipocz]

This all looks good, thank you!

[bsipocz]

devdeps failure is unrelated and has been dealt with separately.

[falkben]

we need to deduplicate the json_data since the events coming from the subscriptions database may have many of the same files.

[snbianco]

That's done later on line 816

[falkben]

i could be misreading the code, i'm not familiar with this codebase, but does remove_duplicate_products only work on uri's? whereas this json data is filesets and datasets?

[snbianco]

Good question and totally fair to ask! remove_duplicate_products actually works on an Astropy Table of products and deduplicates based on the key it’s given (filename). The JSON is converted into a Table earlier in the code, so as long as the JSON format is what we expect, it should work as intended.