Fix problem with Windows file links (backslash in JavaScript string)

This PR was submitted on the symfony/WebProfilerBundle read-only repository and moved automatically to the main Symfony repository (closes symfony/WebProfilerBundle#5).

When you have set php.ini setting xdebug.file_link_format, under Windows this window.location call here isn't escaped properly, so it results in something like:

```HTML
<span class="sf-toolbar-info-method" onclick="window.location='pstorm://open/?url=file://F:\HtDocs\myproject\src\Foo\Core\Controller\PageController.php&amp;line=28';window.event.stopPropagation();return false;">
    pageAction
</span>
```

All backslashes in window.location are treated as escape sequences witch result in an incorrect link:
pstorm://open/?url=file://F:HtDocsmyprojectsrcFooCoreControllerPageController.php&line=28

So clicking this link my IDE (phpStorm) couldn't find that file.

The patch fixes this by escaping the backslashes.