Added "Except" feature

great plugin.

in my case (a really messy site port) I needed to be able to say

– Show every/on selected where except here
– Hide everywhere/on selected except on this page

I messed with the widget logic some and tweaked the JS/css very slightly

https://dl.dropboxusercontent.com/u/81807220/widget-context_103_except.zip

https://ww.wp.xz.cn/plugins/widget-context/