Add offline support for graphiql

There are several scripts and a stylesheet included in `aiohttp_graphql/render_graphiql.py` for the domain `cdn.jsdelivr.net`. The use of this CDN prevents the graphiql interface from being used offline.

The same issue was seen here https://github.com/graphql/graphiql/issues/676

The entire bundle is about +725k to add directly to the package.