Interface to show only read news

[Tiendil]

I see a few variants:

• Replace Show read yes/no with something else, more complex UI
• Add new block Show unread yes/no.

Maybe there are more variants.

First of all, one of variants should be choosen and rationale should be provided.

Only when it will be discussed, we can move to implementation.

[Tiendil]

Also, it would be nice to have a place to add more filters, like "news with no rules applied"