Account:: namespace simplifications and cleanup (#2110)

* Flatten Holding model

* Flatten balance model

* Entries domain renames

* Fix valuations reference

* Fix trades stream

* Fix brakeman warnings

* Fix tests

* Replace existing entryable type references in DB

test/controllers/holdings_controller_test.rb

@@ -0,0 +1,30 @@
+require "test_helper"
+
+class HoldingsControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    sign_in users(:family_admin)
+    @account = accounts(:investment)
+    @holding = @account.holdings.first
+  end
+
+  test "gets holdings" do
+    get holdings_url(account_id: @account.id)
+    assert_response :success
+  end
+
+  test "gets holding" do
+    get holding_path(@holding)
+
+    assert_response :success
+  end
+
+  test "destroys holding and associated entries" do
+    assert_difference -> { Holding.count } => -1,
+                      -> { Entry.count } => -1 do
+      delete holding_path(@holding)
+    end
+
+    assert_redirected_to account_path(@holding.account)
+    assert_empty @holding.account.entries.where(entryable: @holding.account.trades.where(security: @holding.security))
+  end
+end