PLT-2257 Reorganized System Console (#3003)

* Reorganized system console

* Fixed the names of some components

* Fixed timestamp for BrandImageSetting

* Fixed merge issues

* Updated push notification settings to match master branch

* Removed top level setting pages and moved enable Gitlab/LDAP settings onto their respective pages

* Re-added restrictDirectMessage setting to system console

* Re-added email connection test and fixed some margins

* Fixed ESLint errors

* Renamed Authentication > Onboarding to Authentication > Email in the system console

* Renamed Customization > Whitelabeling to Customization > Custom Branding in System Console

* Re-added EnableOpenServer to system console

webapp/sass/components/_save-button.scss

@@ -0,0 +1,7 @@
+@charset 'UTF-8';
+
+.save-button {
+    .glyphicon {
+        margin-right: 10px;
+    }
+}