added align: center property by default
added align: center property by default

git-svn-id: 4c565d0f43a873f8481d9ed76e7b51d47ab13918@15232 ee427ae8-e902-0410-961c-c3ed070cd9f9

Symfony-Plugins/pmHighslideJSPlugin,Symfony-Plugins/pmHighslideJSPlugin