Import/export

[mhauru]

Adds a button in CaseContainer that exports the case as a JSON file, and a button in CaseCreator that can be used to import that same file to create a copy of the case.

Builds on #65, so may be better to merge that first, to see a diff with only the import/export related code.

[mhauru]

https://www.githubstatus.com/ says that triggering actions is down/slow. Assuming they pass once they run, this is ready for review.

[mhauru]

Oh, meant to add a note in the source code: The top right corner of CaseContainer is getting pretty crowded and I'm starting to regret removing the side panel. But maybe sort out where the buttons should be once we settle down a bit with adding more of them?

[coveralls]

Pull Request Test Coverage Report for Build 2035246442

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.9%) to 88.639%

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Totals
Change from base Build 2027395551:	-1.9%
Covered Lines:	1576
Relevant Lines:	1778

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💛 - Coveralls

[nbarlowATI]

Works perfectly (once I figured out I needed to redo npm install to get file-saver).

Yep, would be good to get feedback from users about the best way to deal with proliferation of buttons on the top right, but for now I think this is