feature #4958 Add Twitter Bootstrap form theme example (bocharsky-bw)

This PR was merged into the 2.6 branch.

Discussion
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Add Twitter Bootstrap form theme example

Also add Twitter Bootstrap 3 themes to it (http://symfony.com/blog/new-in-symfony-2-6-bootstrap-form-theme).

Commits
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fa74e41 Add twitter bootstrap form theme example

reference/configuration/twig.rst

@@ -10,13 +10,19 @@ TwigBundle Configuration ("twig")
 
         twig:
             exception_controller:  twig.controller.exception:showAction
+
             form_themes:
 
                 # Default:
                 - form_div_layout.html.twig
 
+                # Bootstrap:
+                - bootstrap_3_layout.html.twig
+                - bootstrap_3_horizontal_layout.html.twig
+
                 # Example:
                 - MyBundle::form.html.twig
+
             globals:
 
                 # Examples: