Account namespace updates: part 4 (transfers, singular namespacing) (#896)

* Move Transfer to Account namespace

* Fix partial resolution due to namespacing plurality

* Make category and tag controllers consistent with namespacing convention

* Update stale partial reference

test/controllers/transfers_controller_test.rb

@@ -1,33 +0,0 @@
-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