Merge branch 'issue_3409' into 'master'

Add ability to revert changes introduced by Merge Requests or Commits

Closes #3409 

See merge request !1990

app/views/projects/commit/_commit_box.html.haml

@@ -16,6 +16,8 @@
     = link_to namespace_project_tree_path(@project.namespace, @project, @commit), class: "btn btn-grouped" do
       = icon('files-o')
       Browse Files
+    - unless @commit.has_been_reverted?(current_user)
+      = revert_commit_link(@commit, namespace_project_commit_path(@project.namespace, @project, @commit.id))
   %div
 
 %p