Make internal error messages more helpful

[stubailo]

This is a good idea overall - we should try to write tests for adverse situations and make sure we print good errors in those cases. Various invalid GraphQL responses, etc.

[deoqc]

When I passed the wrong type to a mutation it failed silently. Easy and useful case for good error message.

mutation: gql`
  mutation onAwesomeMutation($quantity: String!) { # <--- should be Int!
    awesomeMutation (quantity: $quantity)
  }
 `,

[helfer]

I think this issue is too general. It will be much easier to solve these as they come along. Every time someone files an issue we should follow a process in which we do the following:

• Identify the root cause
• Fix the bug/issue
• Write a test for the bug/issue. Make sure to refer to the github issue in the test comments.
• Think about how we can prevent similar issues from even coming up in the future.

In essence when an issue comes up we shouldn't just fix that issue, but also prevent similar issues from occurring again in the future.