DEV: add site setting type group_list for a list of groups

Add a js test

test/javascripts/admin/components/group-list-setting-test.js.es6

@@ -0,0 +1,57 @@
+import componentTest from "helpers/component-test";
+
+moduleForComponent("group-list", { integration: true });
+
+componentTest("default", {
+  template: "{{site-setting setting=setting}}",
+
+  beforeEach() {
+    this.site.groups = [
+      {
+        id: 1,
+        name: "Donuts"
+      },
+      {
+        id: 2,
+        name: "Cheese cake"
+      }
+    ];
+
+    this.set(
+      "setting",
+      Ember.Object.create({
+        allowsNone: undefined,
+        category: "foo",
+        default: "",
+        description: "Choose groups",
+        overridden: false,
+        placeholder: null,
+        preview: null,
+        secret: false,
+        setting: "foo_bar",
+        type: "group_list",
+        validValues: undefined,
+        value: "Donuts"
+      })
+    );
+  },
+
+  async test(assert) {
+    const subject = selectKit(".list-setting");
+
+    assert.equal(
+      subject.header().value(),
+      "Donuts",
+      "it selects the setting's value"
+    );
+
+    await subject.expand();
+    await subject.selectRowByValue("Cheese cake");
+
+    assert.equal(
+      subject.header().value(),
+      "Donuts,Cheese cake",
+      "it allows to select a setting from the list of choices"
+    );
+  }
+});