frontpage (/node) view should use unfiltered text for empty area handler

I don't think any default views shipping with modules should be using the standard area handler as this relies on a filter format. People could change these and boom, you would get no empty text anymore. We should use the custom empty text handler, that just filters the text and does not rely on a particular format (in this case 'plain_text') being available.

This handler was initially added to views to cater for admin_views default views that ship with the module.