Fix for issue #28, fixing security issues on simple server

In `SimpleRestxRequest`, some searches by cookie name was broken `request.getCookies().contains(cookie)` will never return true since `cookie` is a `String` and `request.getCookies()` is a `List<Cookie>`

This leads to critical issue where restxsession cookie cannot be retrieved, totally flawing security handling with restx-server-simple impl.

Provided unit test demonstrating the issue