Add start of IconExtension class

config/services.yml

@@ -3,8 +3,12 @@ services:
         autowire: true
         autoconfigure: true
 
-    pcm_example.example_service:
-        alias: Pcm\ExampleBundle\Service\ExampleService
+    pcm_icon.icon_extension:
+        alias: Pcm\IconBundle\Twig\Functions\IconExtension
         public: true
 
-    Pcm\ExampleBundle\Service\ExampleService: ~
+    Pcm\IconBundle\Twig\Functions\IconExtension:
+        public: false
+        arguments:
+            # $dir:
+                # - '%kernel.project_dir%/public/icons'