Merge branch 'tag-edit-subnav' into 'master'

Fix layout of edit tags page

#### What does this MR do?
Fixes layout of edit tags page

#### Why was this MR needed?
Layout was broken

#### Screenshots (if relevant)
Before:    
![Screen_Shot_2016-08-18_at_1.33.00_PM](/uploads/9e9e52bdc0743971d6e0996e2c2030a0/Screen_Shot_2016-08-18_at_1.33.00_PM.png)
After:    
![Screen_Shot_2016-08-18_at_1.32.08_PM](/uploads/0a4a93508f0c98cb0788a2c70ee33f4e/Screen_Shot_2016-08-18_at_1.32.08_PM.png)


See merge request !5874

app/views/projects/releases/edit.html.haml

+- @no_container = true
 - page_title "Edit", @tag.name, "Tags"
 = render "projects/commits/head"
 
-.row-content-block
+%div{ class: container_class }
+  .sub-header-block.no-bottom-space
     .oneline
       .title
         Release notes for tag
         %strong #{@tag.name}
 
-.prepend-top-default
+
   = form_for(@release, method: :put, url: namespace_project_tag_release_path(@project.namespace, @project, @tag.name), html: { class: 'form-horizontal common-note-form release-form js-quick-submit' }) do |f|
     = render layout: 'projects/md_preview', locals: { preview_class: "md-preview", referenced_users: true } do
       = render 'projects/zen', f: f, attr: :description, classes: 'note-textarea', placeholder: "Write your release notes or drag files here..."
       = render 'projects/notes/hints'
     .error-alert
-    .form-actions.prepend-top-default
+    .prepend-top-default
       = f.submit 'Save changes', class: 'btn btn-save'
       = link_to "Cancel", namespace_project_tag_path(@project.namespace, @project, @tag.name), class: "btn btn-default btn-cancel"