Rename 'target usernames' with 'target recipients' in Composer (#8606)

* Reapply "Rename 'target usernames' with 'target recipients' in Composer"

This reverts commit 9fe11d0fc33850d46d4e1261ba6f66f187652613 which
reverted ebb288dc2cec966fd26ee46f10e1e4d8a596ba5a.

* DEV: Add test for replying to PM

test/javascripts/models/composer-test.js.es6

@@ -396,3 +396,15 @@ QUnit.test("allows featured link before choosing a category", assert => {
   );
   assert.ok(composer.get("canEditTopicFeaturedLink"), "can paste link");
 });
+
+QUnit.test("targetRecipientsArray contains types", assert => {
+  let composer = createComposer({
+    targetRecipients: "test,codinghorror,staff,foo@bar.com"
+  });
+  assert.ok(composer.targetRecipientsArray, [
+    { type: "group", name: "test" },
+    { type: "user", name: "codinghorror" },
+    { type: "group", name: "staff" },
+    { type: "email", name: "foo@bar.com" }
+  ]);
+});