refactoring: extracted IconTool to deal with info/warning/error icons in reports

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608018 13f79535-47bb-0310-9956-ffa450edef68
mark attributes final

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1608019 13f79535-47bb-0310-9956-ffa450edef68