CORS support should be opt-in

[fgrehm]

Some projects don't have a need for supporting old browsers and won't have a need to expose that endpoint.

PS: I'd love to write a spec for this behavior but I was not able to get them running as it complains about not being able to find rails_helper. Any ideas on how to fix this would be greatly appreciated:

 bundle exec rake


-------- ORM: active_record

/Users/fabio/.rbenv/versions/2.2.4/bin/ruby -I/Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib:/Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-support-3.3.0/lib /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/exe/rspec --pattern spec/\*\*\{,/\*/\*\*\}/\*_spec.rb
/Users/fabio/projects/oss/attachinary/spec/features/notes_spec.rb:1:in `require': cannot load such file -- rails_helper (LoadError)
    from /Users/fabio/projects/oss/attachinary/spec/features/notes_spec.rb:1:in `<top (required)>'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/configuration.rb:1327:in `load'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/configuration.rb:1327:in `block in load_spec_files'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/configuration.rb:1325:in `each'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/configuration.rb:1325:in `load_spec_files'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/runner.rb:102:in `setup'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/runner.rb:88:in `run'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/runner.rb:73:in `run'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib/rspec/core/runner.rb:41:in `invoke'
    from /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/exe/rspec:4:in `<main>'
/Users/fabio/.rbenv/versions/2.2.4/bin/ruby -I/Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/lib:/Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-support-3.3.0/lib /Users/fabio/.rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/rspec-core-3.3.2/exe/rspec --pattern spec/\*\*\{,/\*/\*\*\}/\*_spec.rb failed

Cheers!