GitLab

- Use IssuesFinder for the /issues API resouce
- Tests for iid filter in project issues API resource
- Tests for No Milestone filter in issues API resources
  The "No Milestone" case was not previously tested, and the `/issues`
  resource did not support the the `milestone` parameter.
- Return issues where all labels match from the issues and project issues
  API resources, like the group issues resource already does. See
  https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6825#note_17474533

Signed-off-by: Rémy Coutable <remy@rymai.me>