If playlists containing youtube urls are exported or imported, these patches
improve the usability of the playlist.

Lua remembers the original url (i.e. the website _containing_ the content) if
no other url is passed by the lua parsers. It also puts the content title to
the meta-title entry.

XSPF export / import now uses the <info> to deal with the meta-url.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>