core: Minor refactoring of MediaItem class
core: Minor refactoring of MediaItem class

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