Adds PipeEvaluator

[simedw]

Let's you chain multiple evaluators together, main reason is to first try cheap and faster evaluator, such as string-match, and only if they fail go for more expensive ones like semantic similarity.

[andreaazzini]

Is this used anywhere else? If this is to prevent auto-ordering these lines, we have used the # Adding an empty comment to force import order to avoid circular imports comment above, we could potentially use that again?