Re-enable autocomplete for milestones, tags, releases, and wiki

app/assets/javascripts/dispatcher.js

spec/features/issues/form_spec.rb

spec/features/merge_requests/form_spec.rb

spec/features/projects/milestones/new_spec.rb

spec/features/projects/wiki/user_creates_wiki_page_spec.rb

spec/features/projects/wiki/user_updates_wiki_page_spec.rb

spec/features/tags/master_creates_tag_spec.rb

spec/features/tags/master_updates_tag_spec.rb