change system default display order

src/mobile-main.js

@@ -214,7 +214,7 @@ Vue.prototype.$locale = {
             moment.tz.setDefault();
         }
     },
-    getAllTimezones: function () {
+    getAllTimezones: function (includeSystemDefault) {
         const allTimezones = timezone.all;
         const allTimezoneInfos = [];
 
@@ -226,6 +226,14 @@ Vue.prototype.$locale = {
             });
         }
 
+        if (includeSystemDefault) {
+            allTimezoneInfos.push({
+                name: '',
+                utcOffset: this.defaultTimezoneOffset,
+                displayName: i18n.t('System Default')
+            });
+        }
+
         allTimezoneInfos.sort(function(c1, c2){
             const utcOffset1 = parseInt(c1.utcOffset.replace(':', ''));
             const utcOffset2 = parseInt(c2.utcOffset.replace(':', ''));