Add configuration options in the Admin UI for all content set in meta.vm

Right now there are 2 problems:
1) The admin user may decide to add something in HTTP META I+NFO and not include meta.vm and won't even know what he/she looses by doing so
2) We need a way to set a default for each config options.

In practice this means new UI options for:

• Revisit After
• Description
• Keywords
• Rating (not sure what this is why and it should probably be brought by the rating extension?)
• Author
• RSS feeds (we should have a RSS feed extension and that extension should bring it)