Playwright test for --demo

[mccalluc]

• Fix Playwright test for --demo #105

Initially tried to use mocking for this, but couldn't get it to work.

• Filed Do mocks not work inside apps? #119

... but in the end, I think this is a pretty clear approach.

When we handle this:

• When running --demo, don't show the FileUpload component #113

expand the test.

[ekraffmiller]

I don't know what the problem is that you referred to about using mocks, but this seems to work well to test the app being run with and without the demo data. Approving