Updating RssReaderBundle for the new widget system.
adding security on controller.
composer.json
RssReaderController returns 204 response.
form redirection.
Adding claroline-widget-form-cancel class.
Fixing rssform.
Rss errors handling.
Updated core version constraint to 2.0
Merge pull request #2 from claroline/widget-update

Widget update (core 2.0)