Reference cycle issues

Seeing some memory leaks on most routes, most likely due to db requests via query(on: request) which is apparently not best practice.

• [ ] Implement thread-safe controllers
• [ ] Switch to using withPooledConnection(to: .psql) for db queries, like

func routes(_ container: Container) throws -> EngineRouter {
    let router = EngineRouter.default()
    router.get("test") { req in
        return container.withPooledConnection(to: .psql) { ... }
    }
    return router
}