Add option to sync every 30 minutes

Add option to sync "Every 30 minutes" to Sync interval menu in AccountSettingsActivity view

app/src/main/res/values/strings.xml

@@ -315,8 +315,8 @@
     <string name="settings_sync_summary_not_available">Not available</string>
     <string-array name="settings_sync_interval_seconds" translateable="false">
         <item>-1</item>
-        <item>300</item>
         <item>900</item>
+        <item>1800</item>
         <item>3600</item>
         <item>7200</item>
         <item>14400</item>
@@ -324,8 +324,8 @@
     </string-array>
     <string-array name="settings_sync_interval_names">
         <item>Only manually</item>
-        <item>Every 5 minutes</item>
         <item>Every 15 minutes</item>
+        <item>Every 30 minutes</item>
         <item>Every hour</item>
         <item>Every 2 hours</item>
         <item>Every 4 hours</item>