Rename "Integration" tests to "Acceptance" tests.

The term "Acceptance" seems to have won out everywhere and I don't want
our codebase to be confusing.

test/javascripts/integration/groups-test.js.es6

@@ -1,4 +1,5 @@
-integration("Groups");
+import { acceptance } from "helpers/qunit-helpers";
+acceptance("Groups");
 
 test("Browsing Groups", () => {
   visit("/groups/discourse");