CSV Transaction Imports (#708)

Introduces a basic CSV import module for bulk-importing account transactions.

Changes include:

- User can load a CSV
- User can configure the column mappings for a CSV
- Imported CSV shows invalid cells
- User can clean up their data directly in the UI
- User can see a preview of the import rows and confirm import
- Layout refactor + Import nav stepper
- System test stability improvements

test/jobs/import_job_test.rb

@@ -0,0 +1,18 @@
+require "test_helper"
+
+class ImportJobTest < ActiveJob::TestCase
+  include ImportTestHelper
+
+  test "import is published" do
+    import = imports(:empty_import)
+    import.update! raw_csv_str: valid_csv_str
+
+    assert import.pending?
+
+    perform_enqueued_jobs do
+      ImportJob.perform_later(import)
+    end
+
+    assert import.reload.complete?
+  end
+end