Make build artifacts available from the tag screen

Tags are used for publishing releases. Thus it makes sense to make tag build artifacts available from the tag screen.

Right now there is only the [ source code ] download button in tag view:

GitLab could check if build artifacts exist for the tag commit and add [ build artifacts ] download button if they do (like in build view). The button would redirect to the build artifacts browser.

Artifacts in build view:

Mockup (please feel free to change this):

Here's an example .gitlab-ci.yml that creates build artifacts for tags:

release-job:
  script:
    - mvn package -U
  artifacts:
    paths:
    - target/*.war
  only:
    - tags

See further discussion in GitLab blog: https://about.gitlab.com/2016/01/22/gitlab-8-4-released/#comment-2482966985