PLT-3145 Custom Emojis (#3381)

* Reorganized Backstage code to use a view controller and separated it from integrations code

* Renamed InstalledIntegrations component to BackstageList

* Added EmojiList page

* Added AddEmoji page

* Added custom emoji to autocomplete and text formatter

* Moved system emoji to EmojiStore

* Stopped trying to get emoji before logging in

* Rerender posts when emojis change

* Fixed submit handler on backstage pages to properly support enter

* Removed debugging code

* Updated javascript driver

* Fixed unit tests

* Fixed backstage routes

* Added clientside validation to prevent users from creating an emoji with the same name as a system one

* Fixed AddEmoji page to properly redirect when an emoji is created successfully

* Fixed updating emoji list when an emoji is deleted

* Added type prop to BackstageList to properly support using a table for the list

* Added help text to EmojiList

* Fixed backstage on smaller screen sizes

* Disable custom emoji by default

* Improved restrictions on creating emojis

* Fixed non-admin users seeing the option to delete each other's emojis

* Fixing gofmt

* Fixed emoji unit tests

* Fixed trying to get emoji from the server when it's disabled

webapp/utils/utils.jsx

@@ -982,7 +982,10 @@ export function getDisplayName(user) {
 }
 
 export function displayUsername(userId) {
-    const user = UserStore.getProfile(userId);
+    return displayUsernameForUser(UserStore.getProfile(userId));
+}
+
+export function displayUsernameForUser(user) {
     const nameFormat = PreferenceStore.get(Constants.Preferences.CATEGORY_DISPLAY_SETTINGS, 'name_format', 'false');
 
     let username = '';