* Introduces IconsHelper with methods to render SVG icon from a sprite file.
* Adds SVG sprite file with icons mainly from Font Awesome, but also from Material Design Icons and Fluent UI System Icons (based on the work made by Takashi Kato (@tohosaku)).
* Replaces specific icons with new SVG icons.
* Temporarily keep all old CSS icon definitions for backard compatibility.
git-svn-id: https://svn.redmine.org/redmine/trunk@22988 e93f8b46-1217-0410-a6f0-8f06a7374b81
:rhtml and :rxml were finally removed as template handlers at Rails 3.1 RC4.
git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@6559 e93f8b46-1217-0410-a6f0-8f06a7374b81
