Boards: Remove List model coupling
Similar to #285073 (closed), this issue is to remove the dependency that boards have on the List model (https://gitlab.com/gitlab-org/gitlab/blob/master/app/assets/javascripts/boards/models/list.js).
Similar to #285073 (closed), this issue is to remove the dependency that boards have on the List model (https://gitlab.com/gitlab-org/gitlab/blob/master/app/assets/javascripts/boards/models/list.js).