Gallery View & Create Folder uses GraphQL

[chillu]

As a developer, I want to use GraphQL as the API for the asset section, so that I have a consistent content API.

Acceptance criteria:

• Gallery view fetches files via GraphQL
• Folder creation occurs via GraphQL

Exclusions

• File::canView() and Folder::canCreate() permissions are not checked (see GraphQL respects SilverStripe permissions silverstripe-graphql#5)
• Pagination in gallery view (included this now)

Tasks

• Rebase on master
• Pagination in list view (see issue)
• Pagination in gallery view (see issue)
• Sort on files (dropdown and table sort)
• Respect sort when adding new folder after mutation
• Fix folder navigation (currently defaults to undefined) - might be fixed by rebase
• Fix persistence of uploaded files in current view
• Only refetch() once after all uploads complete (not every one)
• Don't show "no items" when loading data (e.g. during pagination)
• Merge custom sort for GraphQL (Allow sort field mapping silverstripe-graphql#24)
• Merge case accessor patch (Improve CaseInsensitiveFieldAccessor silverstripe-graphql#31)
• Test with "select file" in UploadField
• Fix existing unit tests
• Write at least one GraphQL related unit test (e.g. GraphQL query triggered on folder delete)
• Fix behat tests
• Cross browser tests
• Pagination is broken when uploading first file (moved to Pagination is broken when uploading first file #341)
• GraphQL resolver allows duplicating folder names (moved to GraphQL resolver allows duplicating folder names #342)
• PHPDoc for GraphQL classes in asset-admin (moved to PHPDoc for GraphQL classes in asset-admin #343)

Notes

• (Was: Rebase and merge GraphQL work)
• See RFC: Use GraphQL/Apollo for structured data access in the CMS silverstripe-framework#6245. Applies to both framework and asset-admin repos.

[chillu]

Pull request is being prepared in the following branches:
https://github.com/open-sausages/silverstripe-asset-admin/tree/pulls/4.0/graphql
https://github.com/open-sausages/silverstripe-framework/tree/pulls/4.0/graphql

[chillu]

Pull requests for peer review:
silverstripe/silverstripe-framework#6420
#338

[tractorcow]

Reviewing this.