Refactor schema file structure

[KELLOGGS522]

We need to think about refactoring how graphql schema/mutation/queries/types files structure because it is starting to get messy and hard to use.

Here is some examples I found on github of different projects that follow something similar to what is proposed here graphql-python/graphene#545 (comment)

Small project example : https://github.com/cmmartti/fractal-style-schema

Big project example : https://github.com/saleor/saleor

It looks like we have a lot to learn about graphene before we can do it after looking at how these examples do it.

So I say that we finish up #20 and then we can think about learning everything to be ready to do this refactoring.