More keyserver checks

src/freedombone-app-keyserver

     if [ ${#other_keyserver_port} -lt 4 ]; then
         return
     fi
+
+    # Warn if trying to sync
+    if [[ "$other_keyserver_domain" == *"sks-keyservers.net" || "$other_keyserver_domain" == *"gnupg.net" || "$other_keyserver_domain" == *"pgp.com" || "$other_keyserver_domain" == *"pgp.mit.edu" || "$other_keyserver_domain" == *"the.earth.li" || "$other_keyserver_domain" == *"mayfirst.org" || "$other_keyserver_domain" == *"ubuntu.com" ]]; then
+        dialog --title $"Sync with other keyserver" \
+               --msgbox $"\nDon't try to sync with the major keyservers. Your system will be overloaded with an infeasible database size." 8 60
+        return
+    fi
+
     if [[ "$other_keyserver_email" != "pgp-public-keys@" ]]; then
         if [[ "$other_keyserver_email" == *"@"* ]]; then
             if [[ "$other_keyserver_email" == *"."* ]]; then