Add vacation-seconds extension period in advanced class so it is shown only when 'advanced options' option is checked

This is what is shown currently when vacation-seconds is enabled and you try to add a new filter:

![screen shot 2014-09-11 at 13 24 48](https://cloud.githubusercontent.com/assets/8706/4233155/0f028a02-39a7-11e4-91ad-d10e0155ab11.png)

With this simple patch, this options are added as advanced options too:

![screen shot 2014-09-11 at 13 24 22](https://cloud.githubusercontent.com/assets/8706/4233158/1e61e24a-39a7-11e4-97ad-852f57745cdc.png)