Support for class-level validation

This allows for

    $errorElement->addConstraint(new UniqueEntity(['fields' => 'email']));

and similar code without an enclosing ->with().
Update ModelToIdTransformer.php

This is to fix problems with entities with 0 as id, empty will return true if u give 0 as parameter
Update popover allow htl content

Popover is displayed with escaped html tags.
Fix XML support
Fix array_diff comparing nested arrays
Merge pull request #1457 from marekkalnik/fix-extension-filtering

Fix array_diff comparing nested arrays
Merge pull request #1456 from WouterJ/fix_xml

Fix XML support
Merge pull request #1455 from dkorsak/patch-3

Update popover - allow html content
adding unit test for ModelToIdTransformer in the cases where it gets 0 as id
removed test class from the file
Implemented getAdminsByGroup() / hasGroup() functions
Test if identifier is null or not in twig templates, to determine if we have to generate an edit/create form

Fix Issue #1466 create/update routing problem in form creation, when id is 0
Missing coma at the end of the file Ressources/public/base.js
Leading assetic to miss the merge in production env
see : http://stackoverflow.com/questions/9480707/symfony-2-assetic-javascript-compression-causing-errors

Keep up the good wok
Check if route exists and is allowed for short object description
Merge pull request #1471 from EmmanuelVella/short-object-description

Check if route exists and is allowed for short object description
Merge pull request #1470 from gmorel/master

Missing coma at the end of the file Ressources/public/base.js
Added propel documentation
Ask before quitting a page with unsaved changes
Merge pull request #1473 from ClementGautier/propel_support

Added propel documentation
Fix firefox JS bug on viewing revision