Add DataGridExtensionFunctionalTest

Drop travis tests on 2.7 because of "shared" attribute in service container definitions

Fix test AppKernel for symfony 2.8

Set default locale to en-US

Remove useless comment/use statements
Format code

Author: plfort

.travis.yml

@@ -6,9 +6,6 @@ php:
 
 matrix:
   include:
-    - php: 5.6
-      env: |
-        SYMFONY_VERSION=2.7.*
     - php: 5.6
       env: |
         SYMFONY_VERSION=2.8.*