Add ability to filter a question from all filters

[ojchase]

Some questions are utterly ridiculous, and I never want to see them again. e.g. "Cilantro?" I don't want to have to configure that on every filter.

We need some way to mark a question as ignored. All filters should honor this special filter. And #7 is extra important to have implemented.

Workaround: #7 's workaround could be used for existing filters, but honestly the UI would be easier than that. Future filters have no workaround.

[ojchase]

These questions should probably still show up in #21 however.