Can't import a csv file into the app

[jameskerr]

If you try to drag a csv into the app you get this error:

Since the backend supports it, we should enable a csv to be dragged into the app.

A possible workflow is:

1. Import the file
2. If there is an auto detect error, prompt the user for the type of file

[philrz]

FYI, I think this is working now. The attached video shows me successfully importing a CSV file with Brim v0.28.0.

Verify.mp4

[jameskerr]

I'd love a dialog that asks the user which format their data is in to pass to zed load. I've got a csv that it things is zson so it fails with a strange error.

It would also be nice to give a summary of what the auto detect detected.

[philrz]

Since the original spirit of this issue has morphed somewhat, I've opened #2498 to be clearer about where things stand currently. Closing this one since for the general case of importing true CSV into the app, it does indeed work now.