PLT-3143 Added serverside code for custom Emoji (#3311)

* Added model objects for emoji

* Added database tables for emoji

* Added settings for custom emoji

* Added serverside APIs and unit tests for custom emoji

* Added additional validation to catch duplicate emoji names earlier on

* Added additional validation to prevent users from adding emoji as another user

webapp/root.jsx

@@ -73,6 +73,7 @@ import DatabaseSettings from 'components/admin_console/database_settings.jsx';
 import StorageSettings from 'components/admin_console/storage_settings.jsx';
 import ImageSettings from 'components/admin_console/image_settings.jsx';
 import CustomBrandSettings from 'components/admin_console/custom_brand_settings.jsx';
+import CustomEmojiSettings from 'components/admin_console/custom_emoji_settings.jsx';
 import LegalAndSupportSettings from 'components/admin_console/legal_and_support_settings.jsx';
 import ComplianceSettings from 'components/admin_console/compliance_settings.jsx';
 import RateSettings from 'components/admin_console/rate_settings.jsx';
@@ -461,6 +462,10 @@ function renderRootComponent() {
                                 path='custom_brand'
                                 component={CustomBrandSettings}
                             />
+                            <Route
+                                path='custom_emoji'
+                                component={CustomEmojiSettings}
+                            />
                             <Route
                                 path='legal_and_support'
                                 component={LegalAndSupportSettings}