Add "Start a new merge request" option to every commit form

app/assets/javascripts/blob/blob_file_dropzone.js.coffee

app/assets/javascripts/blob/edit_blob.js.coffee

app/assets/javascripts/blob/new_blob.js.coffee

app/assets/javascripts/new_commit_form.js.coffee

app/assets/stylesheets/pages/editor.scss

app/controllers/application_controller.rb

app/controllers/concerns/creates_merge_request_for_commit.rb

app/controllers/projects/blob_controller.rb

app/controllers/projects/tree_controller.rb

app/helpers/merge_requests_helper.rb

app/views/projects/blob/_actions.html.haml

app/views/projects/blob/_new_dir.html.haml

app/views/projects/blob/_remove.html.haml

app/views/projects/blob/_upload.html.haml

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

app/views/projects/blob/new.html.haml

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

app/views/projects/tree/_tree_content.html.haml

app/views/shared/_commit_message_container.html.haml

app/views/shared/_new_commit_form.html.haml