Fixed MopaBootstrap dependency (now optional)

Unable to find template "MopaBootstrapBundle:Form:fields.html.twig" in SonataUserBundle:ChangePassword:changePassword_content.html.twig at line 2.
Merge pull request #360 from mellivora-capensis/patch-1

Fixed MopaBootstrap dependency (now optional)
Added UserManagerProxy
Merge pull request #361 from sylvaindeloux/master

Added proxy for UserManager
Merge branch 'sonata-project/master'