Fixed undefined index notice in readProperty() method (PropertyPath)
[Translation] Added the gettext loaders
[Security] Support removing tokens from a session.
add the ability to set the form prototype name in CollectionType. this will aid in handling nested collections in forms
update variable name to match the option name
make suggested changes for default value
Allow syntax like ``{% render "AcmeDemoBundle:Frontend/Default:index" %}``

Bug fix: yes
Feature addition: yes
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: #2424
[SecurityBundle] Added a way to extend the providers section of the config
[DoctrineBundle] Moved the entity provider service to DoctrineBundle
Added `group_by` to EntityType
`EntityChoiceList` now supports grouping of entities by property path or closure
Added group_by tests for EntityChoiceList
Added group_by test for EntityType
CS - (String) renamed to (string)
Removed Closure support from group_by (PropertyPath strings only)
Added EntityChoiceList test for `group_by` and invalid, deep property paths

This is a common case with optional Entity associations:
  $user->getGroup()->getName()

The property path `group.name` (traversing from the User Entity), when
the User is not assigned to a Group, will throw an UnexpectedTypeException.
This is caught so that the User can still be listed as an option, just without
any nesting.
CS - camelCase & curly braces
[Security] Check for request's session before attempting writes.
[Doctrine] Remove AbstractDoctrineBundle and move code into Doctrine Bridge
[Security] Fix typo in init:acl command name