Allow to specify keywords to aiohttp Application

[lbolla]

This allows to specify aiohttp.Application kws: see https://docs.aiohttp.org/en/stable/web_reference.html#aiohttp.web.Application

E.g.: for middlewares

        cirrina.Server(app_kws={
            'middlewares': [error_middleware]
        })

[szakalboss]

https://docs.aiohttp.org/en/stable/web_advanced.html#middlewares

[lbolla]

https://docs.aiohttp.org/en/stable/web_advanced.html#middlewares

@szakalboss What is this comment supposed to mean? Would you elaborate?