improve marketplace packages release notes display

1. currently there is no formatting and carriage return should be replaced with a HTML <br> tag.
2. this cannot be done upfront since Nuxeo escapes the characters for security reasons. Though it could be done afterwards by reformatting the description in the package document description.
3. ideally, this could then be applied to every Nuxeo package already published

https://connect.nuxeo.com/nuxeo/site/marketplace/package/nuxeo-7.10-HF23

Also, this could be done with Markdown.