Transaction transfers, payments, and matching (#883)

* Add transfer model and clean up family snapshot fixtures

* Ignore transfers in income and expense snapshots

* Add transfer validations

* Implement basic transfer matching UI

* Fix merge conflicts

* Add missing translations

* Tweak selection states for transfer types

* Add missing i18n translation

test/controllers/transfers_controller_test.rb

@@ -0,0 +1,33 @@
+require "test_helper"
+
+class TransfersControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    sign_in users(:family_admin)
+  end
+
+  test "should get new" do
+    get new_transfer_url
+    assert_response :success
+  end
+
+  test "can create transfers" do
+    assert_difference "Transfer.count", 1 do
+      post transfers_url, params: {
+        transfer: {
+          from_account_id: accounts(:checking).id,
+          to_account_id: accounts(:savings).id,
+          date: Date.current,
+          amount: 100,
+          currency: "USD",
+          name: "Test Transfer"
+        }
+      }
+    end
+  end
+
+  test "can destroy transfer" do
+    assert_difference -> { Transfer.count } => -1, -> { Transaction.count } => 0 do
+      delete transfer_url(transfers(:credit_card_payment))
+    end
+  end
+end