[CR] Advanced filter/priority stuff. Tweaked filter exclusion logic

Added some advanced flags in show_items_nearby filter/priorty system.
Also tweaked the filter exclude to only exclude tokens that have '-' preceeding them.

I'd like some guys to play around with this and let me know what they think.
I've documented the new features in the little window below the item list when you select 'f'ilter or -/+ priorities.