core: add begin, commit and rollback methods
core: add begin, commit and rollback methods

Pelagicore/Media-Manager-Rygel-patched,luisbg/rygel,GNOME/rygel,Tarnyko/rygel,jku/rygel,Pelagicore/Media-Manager-Rygel-patched,GNOME/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,jku/rygel,Tarnyko/rygel