Improve changelog

Improve the comment field in content editor and change log list and details are refactored based on last comment thread on PR #1289

PS. the `app/resources/translations/pt/messages.pt.yml` change end of line from CRLF to LF
Why not pick an icon from [Font Awesome](http://fortawesome.github.io/Font-Awesome/)? I'd rather use a vector icon, for thos of us who are on smartphones, tablet or retina displays. ;-)