refactored ex NOOP filter & specs into filter base specs

the NOOP filter is now a dynamically defined class into the `spec/filters/base_spec.rb` and the Plugin#lookup method has been adjusted to support dynamically defined plugins.
personally I am not a big fan of spaces around braces {} - just like for parenthesis () where we don't usually add spaces. but for the sake of consistency I'll add them - we can have (or not :P) this styling discussion elsewhere :)