* add GitHub GraphQL api initial support
* support mutiple backends for e2e tests - initial commit
* add github backend e2e test (currently skipped), fix bugs per tests
* refactor e2e tests, add fork workflow tests, support fork workflow in GraphQL api
* remove log message that might contain authentication token
* return empty error when commit is not found when using GraphQL (align with base class)
* disable github backend tests
* fix bugs introduced after rebase of GraphQL and OpenAuthoring features
* test: update tests per openAuthoring changes, split tests into multiple files
* fix: pass in headers for pagination requests, avoid async iterator as it requires a polyfill on old browsers
* test(e2e): disable github backend tests
* Fix handling of displayURLs which are strings
* Add fromFetchArguments to unsentRequest
* Add parseLinkHeader to backendUtil
* Handle paginated endpoints in GitHub API
* Rename fork workflow to Open Authoring across the whole repo
* Fixes for bugs in GitHub API introduced by Open Authoring changes
* Fix getDeployPreview
* Fix incorrect auth header formatting GitHub implementation
cf. https://github.com/netlify/netlify-cms/pull/2456#discussion_r309633387
* Remove unused and broken method from GitHub API
cf. https://github.com/netlify/netlify-cms/pull/2456#discussion_r308687145
* Fix editorialWorkflowGit method in GitHub API
* Request published entry content from origin repo
* Better error when deleting a published post in Open Authoring
* Rename to Open Authoring in fork request message
Also adds a note to the fork request message that an existing fork of
the same repo will be used automatically.
* fix linting
