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/components/admin_console/admin_sidebar.jsx

@@ -532,6 +532,16 @@ export default class AdminSidebar extends React.Component {
                                 }
                             >
                                 {customBranding}
+                                <AdminSidebarSection
+                                    name='custom_emoji'
+                                    title={
+                                        <FormattedMessage
+                                            id='admin.sidebar.customEmoji'
+                                            defaultMessage='Custom Emoji'
+                                        />
+
+                                    }
+                                />
                                 <AdminSidebarSection
                                     name='legal_and_support'
                                     title={