middleware: add basic response middleware

This commit adds a basic response middleware for both announces, and scrapes.

Completes one of the tasks in #145

server/store/middleware/response/README.md

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+## Response Middleware
+
+This package provides the final response for a chain of middleware using the “store” package.
+
+### `store_response`
+
+The `store_response` middleware uses the peer data stored in the peerStore to create a response for the request.
+
+### Important things to notice
+
+This middleware is very basic, and may not do everything that you require.