New right side gutter design.

app/assets/javascripts/issuable_context.js.coffee

app/assets/stylesheets/framework/sidebar.scss

app/assets/stylesheets/framework/variables.scss

app/assets/stylesheets/pages/issuable.scss

app/helpers/application_helper.rb

app/helpers/nav_helper.rb

app/views/layouts/_page.html.haml

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

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

app/views/shared/issuable/_sidebar.html.haml