Diffs will create button/diff form on demand no on server side

CHANGELOG

app/assets/javascripts/diff.js.coffee

app/assets/javascripts/files_comment_button.js.coffee

app/assets/javascripts/merge_request_tabs.js.coffee

app/controllers/projects/compare_controller.rb

app/controllers/projects/merge_requests_controller.rb

app/helpers/notes_helper.rb

app/mailers/emails/projects.rb

app/views/projects/diffs/_diffs.html.haml

app/views/projects/diffs/_line.html.haml

app/views/projects/diffs/_match_line_parallel.html.haml

app/views/projects/diffs/_parallel_view.html.haml

app/views/projects/show.html.haml

features/project/commits/diff_comments.feature

features/steps/shared/diff_note.rb

spec/features/notes_on_merge_requests_spec.rb