Run php-cs-fixer and enable PHP CS fixer on Scrutinizer

Add checks

Set phpcs to PSR2

Run php-cs-fixer
Fix some issues
we do not use milestones for this bundle. fix #171
Merge pull request #175 from FriendsOfSymfony/roadmap-readme

Update README: we do not use milestones for this bundle
Merge pull request #163 from FriendsOfSymfony/cs-fixer

Enable PHP CS fixer on Scrutinizer
Moving the user context logic out of the kernel inheritance hierarchy.
cleanups from feedback
Added subscriber options to HttpCache

Based on #177, ref #170

This PR adds 1 option that one can add in their `getOptions()`:

* `fos_native_subscribers`: bit options to activate/deactivate subscribers provided by FOSHttpCacheBundle

> By default **all native subscribers are activated** (`HttpCache::SUBSCRIBER_ALL`).

**ALL native subscribers EXCEPT the user context one**
```php
public function getOptions()
{
    return [
        'fos_native_subscribers' => self::SUBSCRIBER_ALL | ~self::SUBSCRIBER_USER_CONTEXT
    ]
}
```

**NO native subscribers**
```php
public function getOptions()
{
    return [
        'fos_native_subscribers' => self::SUBSCRIBER_NONE
    ]
}
```

**ONLY user context subscribers**
```php
public function getOptions()
{
    return [
        'fos_native_subscribers' => self::SUBSCRIBER_USER_CONTEXT
    ]
}
```

**User context subscriber AND Foo subscriber**
```php
public function getOptions()
{
    return [
        'fos_native_subscribers' => self::SUBSCRIBER_USER_CONTEXT | self::SUBSCRIBER_FOO
    ]
}
```
Fixed fatal error due to namespace collision
cleanup on user context subscriber