Templating changes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | no (will pass when sonata-project/SonataBlockBundle#80 is merged)
| Fixed tickets | -
| License       | MIT
| Doc PR        | coming soon

As discussed in symfony-cmf/CoreBundle#62 It shoud not be merged until the upstream SonataBlockBundle PR is merged.