Generate args prepending context object name

[galales]

This should fix #367 and fix #552

I had to pass the ObjectTypeDefinition to the writeArguments function to concatenate the required name.
In order to avoid having classes with "Mutation", "Query" and "Subscription" prefix, objects definitions have been checked against reservedType function.
When calling writeField, checks are done also on schema definition and union types. I don't think it is required in this case, but correct my if I'm wrong.

Let me know if you think additional changes are required

[ghostdogpr]

Looks very good! 2 issues fixed for the price of 1 😄