[TwigBridge] Replace default list style to icon
[Serializer] Handle circular references
feature #12098 [Serializer] Handle circular references (dunglas)

This PR was merged into the 2.6-dev branch.

Discussion
----------

[Serializer] Handle circular references

| Q             | A
| ------------- | ---
| Bug fix?      | Yes: avoid infinite loops. Allows to improve #5347
| New feature?  | yes (circular reference handler)
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | symfony/symfony-docs#4299

This PR adds handling of circular references in the `Serializer` component.
The number of allowed iterations is configurable (one by default).
The behavior when a circular reference is detected is configurable. By default an exception is thrown. Instead of throwing an exception, it's possible to register a custom handler (e.g.: a Doctrine Handler returning the object ID).

Usage:
```php
use Symfony\Component\Serializer\Normalizer\GetSetMethodNormalizer;
use Symfony\Component\Serializer\Serializer;

class MyObj
{
    private $id = 1312;

    public function getId()
    {
        return $this->getId();
    }

    public function getMe()
    {
        return $this;
    }
}

$normalizer = new GetSetMethodNormalizer();
$normalizer->setCircularReferenceLimit(3);
$normalizer->setCircularReferenceHandler(function ($obj) {
    return $obj->getId();
});

$serializer = new Serializer([$normalizer]);
$serializer->normalize(new MyObj());
```

Commits
-------

48491c4 [Serializer] Handle circular references
minor #12164 [TwigBridge] Replace default list style to icon (Macsch15)

This PR was merged into the 2.6-dev branch.

Discussion
----------

[TwigBridge] Replace default list style to icon

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Replaces default list style in **bootstrap_3_layout.html.twig** to icon.
Requires Glyphicons from Bootstrap 3.

Before:
![2014-10-07 11-55-50](https://cloud.githubusercontent.com/assets/1592053/4540807/d6f8eb46-4e0b-11e4-82bf-77b56fd1d17c.png)

After:
![2014-10-07 11-55-07](https://cloud.githubusercontent.com/assets/1592053/4540810/e02fe048-4e0b-11e4-9f3b-69902c0ae32b.png)

Commits
-------

9a0b2cc [TwigBridge] Replace default list style to icon
[Form][WebProfiler] Empty form names fix

When a Form had no name, the markup was broken in the profiler,
making the form tree ugly.