Moves specs over to using shared_example to avoid duplication..

We don't fully support it yet, so make sure we don't create any by
mistake.

Also add iteration field under GraphQL project type

The plan for RSpec 4.0 is to disable monkey patching:
https://rspec.info/blog/2013/07/the-plan-for-rspec-3/#zero-monkey-patching-mode

This commit stops using RSpec monkey patching:
https://relishapp.com/rspec/rspec-core/docs/configuration/zero-monkey-patching-mode

Add the creation of SystemNotes when an Issue gets their iteration
changed or removed.

Adds a GraphQL type for Sprints as well as adding it to
Issues/Projects/Groups and adding an Issue::SetSprint and
Group::CreateSprint mutators.