Warn with yellow toast when result of Data Import is unknown

When importing a record by posting to copycat/imports (mod-copycat), there are three categories of response:

1. 200 OK with an internalIdentifier in the response
2. 200 OK without an internalIdentifier
3. Any other HTTP code.

The meanings of these responses are:

1. New record successfully important, and its UUID is known.
2. New record queued for import, but its UUID was not known by the time mod-copycat returned its response. (This means it has polled several times for the new record, but not seen it.)
3. Some kind of hard error, such as misconfiguration of the Z39.50 target details.

We want the UI to handle these responses as follows:

1. Show a green toast stating that the record was imported successfully, and redirect to the new record.
2. Show a yellow toast stating that the record was queued for import.
3. Red toast stating the error.