Config option to disable Imagic use of SVG for Avatars

Config option to disable Imagic use of SVG for Avatars: From time to time there are problems generating automatic Avatars. This is mainly due to the combination of PHP modules with specific combination of ImageMagic and Freetype. When depending on a hosting provider, it might not be an option to change the versions of IMagic and Freetype used for a specific PHP version.