allow delegation of block rendering

ref #12

In a template, you can now allow rendering of a block from other bundle.

The layout template must explicitly call the rendering of other block,
with the twig function

```
chill_delegated_block('block_name', { 'array' : 'with context' } )
```

This will launch an event
`Chill\MainBundle\Templating\Events\DelegatedBlockRenderingEvent` with
the event's name 'chill_block.block_name'.

You may add content to the page using the function
`DelegatedBlockRenderingEvent::addContent`.

Resources/config/services.yml

@@ -51,6 +51,13 @@ services:
         tags:
             - { name: twig.extension }
             
+    chill.main.twig.delegated_block:
+        class: Chill\MainBundle\Templating\DelegatedBlockRenderingTwig
+        arguments:
+            - "@event_dispatcher"
+        tags:
+            - { name: twig.extension }
+            
     chill.main.twig.csv_cell:
         class: Chill\MainBundle\Templating\CSVCellTwig
         tags: