Add method to task to retreive the icon

This makes a task somewhat more useful outside of the
context of a taskwindow.

Reviewed-by: dt

src/plugins/projectexplorer/taskwindow.h

@@ -86,6 +86,9 @@ struct PROJECTEXPLORER_EXPORT Task {
     // doesn't work if you split it up, nor are our parsers
     // anywhere near being that good
     QList<QTextLayout::FormatRange> formats;
+
+    /// Get the icon used to represent this task
+    QIcon icon() const;
 };
 
 class PROJECTEXPLORER_EXPORT TaskWindow : public Core::IOutputPane