Modal to display ingest errors

[jameskerr]

When the user clicks on the errors counter, we'll display a modal with a scrolling list of all the errors.

[philrz]

Verified in Brim commit 1fae48f.

In the attached video, I drag in a log file that I know is going to generate a warning (a single JSON line {"foo": "bar"}). Brim now shows a message "Ingest failed with warnings" and a warning icon with a count. When clicked, it pops up a modal with the error detail, which in this case is the accurate message /Users/phil/Desktop/ingest/foo.ndjson: line 1: missing path field.

Verify.zip

Thanks @jameskerr!