Merge branch 'rs-opengraph' into 'master'

app/assets/images/brand_logo.png

app/assets/images/gitlab_logo.png

app/helpers/page_layout_helper.rb

app/models/concerns/issuable.rb

app/views/layouts/_head.html.haml

app/views/projects/issues/show.html.haml

app/views/projects/merge_requests/_show.html.haml

app/views/projects/milestones/show.html.haml

app/views/users/show.html.haml

spec/helpers/page_layout_helper_spec.rb

spec/models/concerns/issuable_spec.rb