Review schema roots naming

[mariogarcia]

At the moment DSL.schema queries are defined like:

GraphQLSchema schema = DSL.schema {
  query('QueryRoot') {
    field('byYear') { }
    field('byActor') { }
  }
}

But I would say that if we're adding queries definitions inside one query root, it would make more sense to have defined it like:

GraphQLSchema schema = DSL.schema {
  queries('QueryRoot') {
    field('byYear') {}
    field('byActor') { }
   }
}

And given the fact that we only add one query root and one mutation root we could omit the name of the query root (and implicityly call them QueryRoot and MutationRoot)

GraphQLSchema schema = DSL.schema {
  queries {
    field('byYear') {}
    field('byActor') { }
  }
  mutations {
    field('insertMovie') { }
  }
}

or:

GraphQLSchema schema = DSL.schema {
  queries {
    addField filmGraphQL.getByYearQuery()
    addField filmGraphQL.getByActorQuery()
  }
  mutations {
    addField filmGraphQL.getInsertMutation()
  }
}

Some final thoughts:

• There should be two overwritten methods queries(Closure) and queries(String, Closure) in case something would want to name his/her query root with a custom name
• Although I thought to change field by query and addField to addQuery however the type of object created or passed as an argument is a field, not a query. That would have led the API a little bit incoherent.