Support for class-level validation

This allows for

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

and similar code without an enclosing ->with().
Add desctiption for change default route in ListAction
The preg_replace() /e modifier is deprecated from PHP5.5.0.
Update README.md
Added PHP 5.5 to .travis.yml
Merge pull request #1424 from pulzarraider/patch-2

Added PHP 5.5 to .travis.yml
Merge pull request #1423 from pulzarraider/patch-1

Update README.md
Merge pull request #1421 from spolischook/update-doc-routing

Add desctiption for change default route in ListAction
Updated PT translations
Merge pull request #1425 from danielcsgomes/master

Updated PT translations
FOSUB github URL changed
Updated italian translation
Merge pull request #1430 from andreadelfino/translation-it

Updated italian translation
documentation update on sonata_type_collection
Merge pull request #1432 from tiagojsag/collection_type_docs

documentation update on sonata_type_collection
Fix breadcrumbs for custom routes when subject is empty

Hi. When I open my custom routes, there is no label in breadcrumbs for it, because subject is empty.
Update configuration.rst

the sonata_admin.templates section wasn't full (it's now aligned with Templates documentation page)
Update templates.rst

sonata_admin.templates.dashboard was missing
Merge pull request #1443 from net02/patch-2

Updated documentation
wrap nav menu in block for easier customization