Support for Schema autocomplete in codemirror-graphql

I'm working on top of what it's already supported on codemirror-graphql and adding some new stuff to support autocomplete, here's some videos of what I have so far: https://twitter.com/sebas5384/status/1284981079636574208?s=20

For now the `graphql` mode is doing an excellent job, though things like multiline comments are not supported so I'll have to add that later so users can document their schema.

Hope to upload the code by the end of this week, maybe as a PR, don't know yet.

I know this project is moving towards Monaco editor, but I guess the autocompletion could be reused.