fix #1237 remove unreachable types from generated code

[vikstrous]

This PR removes unreachable objects, inputs, interfaces, unions, scalars, and enums from the schema right after parsing it. It doesn't try to remove unused directives.

Existing tests did a reasonable job at covering the changes, but this does need more testing. I added unreachable.graphql with an object, an input, an interface, an union, a scalar, and an enum.

I need feedback on what to do with built in types like Int and if this warning message makes sense:

Warning: unreachable types: AIt, AbIt, Content_Child, Content_Post, Content_User, EmbeddedDefaultScalar, EmbeddedPointer, LoopA, LoopB, Map, UnreachableEnum, UnreachableInput, UnreachableInterface, UnreachableObject, UnreachableScalar, UnreachableUnion, XXIt, XxIt, asdfIt, iIt

I could use some help with the diff in the generated resolver.go code. There's some formatting issue?

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[coveralls]

Coverage increased (+0.4%) to 66.485% when pulling 91b9ff4 on vikstrous:unreachable into a3c38c6 on 99designs:master.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[frederikhors]

Nope

[StevenACoffman]

@vikstrous can you resolve conflicts and see if that passes the linter this time?

[vikstrous]

continued in #2139