Add margin to pages where is no header

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/groups/edit.html.haml

 - header_title group_title(@group, "Settings", edit_group_path(@group))
 - @blank_container = true
 
-.panel.panel-default
+.panel.panel-default.prepend-top-default
   .panel-heading
     Group settings
   .panel-body

app/views/groups/group_members/index.html.haml

@@ -2,7 +2,7 @@
 - header_title group_title(@group, "Members", group_group_members_path(@group))
 - @blank_container = true
 
-.group-members-page
+.group-members-page.prepend-top-default
   - if current_user && current_user.can?(:admin_group_member, @group)
     .panel.panel-default
       .panel-heading

app/views/groups/projects.html.haml

 - page_title "Projects"
 - header_title group_title(@group, "Projects", projects_group_path(@group))
 
-.panel.panel-default
+.panel.panel-default.prepend-top-default
   .panel-heading
     %strong= @group.name
     projects:

app/views/projects/project_members/index.html.haml

@@ -2,7 +2,7 @@
 = render "header_title"
 - @blank_container = true
 
-.project-members-page
+.project-members-page.prepend-top-default
   - if can?(current_user, :admin_project_member, @project)
     .panel.panel-default
       .panel-heading