Implement type/union suppression (#859)

* Implement type/interface/enum/union suppression

* Remove out-of-place InputSchemaStrings class

* Fix type annotation

* Implement error checking to prevent unsupported suppressions

* Remove outdated comment

* Raise error onuppressing interface implementation

* Nits

* lint

* Reorder functions

* Update CascadingSuppressionError message

* start lint

* Fix lint

* typo

* Fix mypy errors around GraphQL-core's type-hint

* mypy attempted fix with REMOVE set to Ellipsis

* Formatting

* fix cascading init header

* Replace return None with return IDLE

* Add missing words

* Refactor helper function to return IDLE value when appropriate

* Fix comments

* Add module docstring

* Fix bug with union cascading check

* Nits

* Update renamings argument description

* add missing whitespace

* satisfy mypy

* Fix docstring paste mistake

* Fix wording for cascading error explanation

* Correct docstrings for cascading visitor

* Add note about superclass error

* Clarify file docstring

* Fix rename_schema docstring

* Remove unnecessary comment

* Improve cascading error message

* fix comments

* typo

* Remove unnecessary arg

* Refactor to clarify object name

* address nits

* Update Pipfile to use graphql-core >= 3.1.2

* Narrow type hints with graphql-core update

* Remove null check

Issue graphql-python/graphql-core#98 fixed in
graphql-core 3.1.2

* Update scalar renaming documentation

* Indicate suppression along with renaming in comments

* Use bullet points in CascadingSuppressionError

* Add class docstrings describing error-checking visitor usage

* lint

* Address comments

Pipfile

@@ -39,7 +39,7 @@ sphinx = ">=1.8,<2"
 [packages]  # Make sure to keep in sync with setup.py requirements.
 arrow = ">=0.15.0,<1"
 funcy = ">=1.7.3,<2"
-graphql-core = ">=3.1,<3.2"  # minor versions sometimes contain breaking changes
+graphql-core = ">=3.1.2,<3.2"  # minor versions sometimes contain breaking changes
 pytz = ">=2017.2"
 six = ">=1.10.0"
 sqlalchemy = ">=1.3.0,<2"