fix global blocks configuration + add some examples:

 * media_advanced block is excluded from left zones
 * page_children block is excluded from containers
Add text and link to the documentation on the sandbox homepage
update prestacmscore deps
Merge pull request #50 from MatCottet/add_example_blocks_configuration

fix global blocks configuration + add some examples
update composer.lock to use the last modification on presta/cms-core-bundle for container fixtures
Merge branch 'master' into add_container_demonstration

Conflicts:
	composer.lock
Merge pull request #52 from prestaconcept/add_container_demonstration

Add text and link to the documentation on the sandbox homepage