play queue.  Fixes #329958.

* shell/Makefile.am:
* shell/rb-playlist-manager.h:
* shell/rb-playlist-manager.xml:
* shell/rb-playlist-manager.c: (save_playlist_response_cb),
(rb_playlist_manager_get_playlists),
(rb_playlist_manager_get_playlist_names), (_get_playlist_by_name),
(rb_playlist_manager_create_static_playlist),
(rb_playlist_manager_delete_playlist),
(rb_playlist_manager_add_to_playlist),
(rb_playlist_manager_remove_from_playlist),
(rb_playlist_manager_export_playlist):
Add org.gnome.Rhythmbox.PlaylistManager dbus interface, with methods
to create, delete, list, modify, export, and import  static playlists.

* shell/main.c: (main): Register playlist manager object with dbus.

* shell/rb-shell.h:
* shell/rb-shell.xml:
* shell/rb-shell.c: (rb_shell_get_playlist_manager),
(rb_shell_get_playlist_manager_path), (rb_shell_add_to_queue),
(rb_shell_remove_from_queue):  Provide dbus access to the playlist manager
object, and implement the addToQueue and removeFromQueue methods.

* sources/rb-playlist-source.c: (rb_playlist_source_save_playlist):
* sources/rb-playlist-source.h: Add flag to choose between PLS and M3U
formats.