Error on transaction import is not shown

[morremeyer]

Describe the bug
When trying to import a transaction that leads to an error, the "Successfully imported" banner is shown, the transaction is removed from the import and the

To Reproduce
Steps to reproduce the behavior:

1. Start an import
2. Use on-budget accounts for both source and destination accounts and set an envelope
3. Click import
4. See that the transaction is removed from the import and the "Successfully imported" banner shown
5. Check transactions and see that it does not exist (since it is rejected by the backend with a 400 Bad Request)

Expected behavior

• The error returned by the backend is shown
• The transaction is not removed from the import