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.
and I suppose we don't want that by the principle of least surprise, if you dynamically define a plugin class that also exists as a file you probably mean to have the dynamically one supersede the file based one.