[RFC][WIP][2.3] Cache Bundle

Bug fix: no
Feature addition: yes
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: #1513, #3211
License of the code: MIT
Documentation PR: ~
Todo: 
- feedback from GH;
- add create documentation PR for the component;
- fix any CS break;
- fix Configuration WTFs as it's the first time I use the Configuration component
- optimizations?

Hello,

This is the bundle that is 'missing' from the previous PR and it is also with the Request For Comments status.

I'll try and add the remaining things from the TODO list in the specified order.

At least for now I don't care about coding style breaks and so on, I think it's the least important thing right now (don't worry, I'll fix everything, if anything, before merging), so please don't comment about it!

As a last thing, I really want to finish this in time for 2.2 release/feature freeze so if you want to help me out, any and all PRs are welcomed.

Thank you!


Configuration:

```yml
cache:
    drivers:
        apc:          ~
        memcached:
            server:
                host: 127.0.0.1
                port: 11211
    instances:
        apc1:
            type:     apc
        memcached1:
            type:     memcached
        memcached2:
            type:     memcached
            server:
                host: 127.0.0.1
                port: 11212
```

```php
$cacheObject = new CacheItem('demo3', 'demo2.4', 600);

$this->get('cache.apc1')->set($cacheObject);
var_dump($this->get('cache.apc1')->get('demo3'));

$this->get('cache.memcached1')->set($cacheObject);
var_dump($this->get('cache.memcached1')->get('demo3'));
```

Demo available here: http://sf2demo.rodb.ro/app_dev.php/