CORS and REST

[subdee]

As metioned in #303 , CORS might sometimes need to be used for cross-domain AJAX calls. Some libraries like Angular require certain headers to be present for non-GET and non-POST requests otherwise they error out. Some headers are outlined here: https://developer.mozilla.org/en-US/docs/HTTP/Access_control_CORS#The_HTTP_response_headers

My proposal would be to have a CORS flag that if enabled, it will create and send those headers along. I have currently implemented this in the beforeAction of my controller but I can create a Pull request for review and suggestions, if it's considered.

[pgaultier]

This feature has been added with yii\filters\Cors