Unfold "latest" pipelines to show previous pipelines which makes latest tag unneeded

latest tag is unnecessary if we are able to fold the previous pipeline under the most recent one.. effectively hiding them, making them appear at the touch of a button inline.

as discussed here: https://gitlab.com/gitlab-org/gitlab-ce/issues/21454#note_15259240

this is most useful here: https://gitlab.com/gitlab-org/gitlab-ce/pipelines

and should probably follow this design:

cc: @markpundsack