Fix Media compatibilty

As admin dev master moved to 2.2 we need to stay in 2.1 if we want to 
work with SonataMediaBundle 
which depends on notification 2.1 
which depends on admin 2.1
Update composer.json
Merge pull request #85 from nicolas-bastien/patch-1

Fix Media compatibilty
fixed rendering of the tree for Symfony2.2, minor cleanups
Merge pull request #87 from sonata-project/symfony_2_2_compat

fixed rendering of the tree for Symfony2.2, minor cleanups
basic type
Merge remote-tracking branch 'origin/master' into tree_manager_type
Merge pull request #89 from liip-forks/tree_manager_type

Tree manager type
use route instead of calling the controller directly
Merge pull request #90 from liip-forks/tree_manager_type

use route instead of calling the controller directly
use new overlay options for TreeEditing
Merge remote-tracking branch 'origin/master' into use_overlay_option
made overlay options configurable
handle missing document in getChildren()
Merge pull request #91 from liip-forks/use_overlay_option

Use overlay option for tree editing