58404 - add change log


58404 - add spec


58404 - add more spec to test depth 2


58404 - fix spec


58404 - fix rubocop


58404 - refactor the code by Bob's advice


58404 - revert changes of all_graphql_fields_for


58404 - change text only


58404 - fix rspec according to gitlab's standard


58404 - revert previous spec


58404 - fix rubocop

With this we only check abilities on the rendered edges of a GraphQL
connection instead of all the nodes in it.

It makes all Types::BaseField default to a complexity of 1.

Queries themselves now have limited complexity, scaled
to the type of user: no user, authenticated user, or an
admin user.

This is mainly the setup of mutations for GraphQL. Including
authorization and basic return type-structure.

This adds Keyset pagination to GraphQL lists. PoC for that is
pipelines on merge requests and projects.

When paginating a list, the base-64 encoded id of the ordering
field (in most cases the primary key) can be passed in the `before` or
`after` GraphQL argument.

- All definitions have been replaced by classes:
  http://graphql-ruby.org/schema/class_based_api.html
- Authorization & Presentation have been refactored to work in the
  class based system
- Loaders have been replaced by resolvers
- Times are now coersed as ISO 8601

By specifying a presenter for the object type, we can keep the logic
out of `GitlabSchema`.

The presenter gets initialized using the object being presented, and
the context (including the `current_user`).