Allow data URL in CSP config for images

app/config/config_prod.yml

@@ -95,6 +95,7 @@ nelmio_security:
             img-src:
                 - 'self'
                 - 'https:'
+                - 'data:'
                 - 'http://www.google-analytics.com/'
             style-src:
                 - 'self'