Filter improvement suggestion

[Alcides Soares Filho]

I suggest to add a new filter option that would be very usefull: <non choosen posts>.

This would help authors with many posts to avoid reinclude post already choosen. Second, this would clean the avaialable residual posts list, facilitating the inclusion of not yeat choosen posts in the parts.

I dont know it is easy in terms of programming, but it would be a great feature...

I hope this suggestion can contribute to this great plugin.