Drop support for sonata cache in favor for symfony/cache

[wbloszyk]

Related to:
sonata-project/SonataCacheBundle#279
sonata-project/cache#49

composer why sonata-project/cache-bundle

sonata-project/sandbox      dev-master  requires  sonata-project/cache-bundle (^2.4)    
sonata-project/page-bundle  3.21.0      requires  sonata-project/cache-bundle (^2.4.1)  

composer why sonata-project/cache

sonata-project/block-bundle  3.22.0  requires  sonata-project/cache (^1.0 || ^2.0)    
sonata-project/cache-bundle  2.4.2   requires  sonata-project/cache (^1.0.3)          
sonata-project/page-bundle   3.21.0  requires  sonata-project/cache (^1.0.3 || ^2.0)  

In sonata-project/block-bundle only Sonata\BlockBundle\Templating\Helper\BlockHelper is using cache optionally. So it will be easy to add another cache system.

In sonata-project/page-bundle will be more work which should be done in some order:

• make sonata-project/cache-bundle opional
• add symfony/cache
• deprecate sonata/cache

[core23]

Refs: sonata-project/SonataBlockBundle#663

The problem is, that the sonata cache is not only a simple cache. It does some other things too.

[jordisala1991]

I think this can be closed, BlockBundle is already done, and only remains pageBundle, being tracked here: sonata-project/SonataPageBundle#1096