change descriptions for mpd statistics since they can be misleading

mpd doesn't report unique albums, it only counts
different album names. same for artists.

different name for number of songs is just cosmetic.

src/server_info.cpp

@@ -108,9 +108,9 @@ void ServerInfo::Update()
 	*w << fmtBold << U("Total playtime: ") << fmtBoldEnd;
 	ShowTime(*w, Mpd.DBPlayTime(), 1);
 	*w << '\n';
-	*w << fmtBold << U("Number of artists: ") << fmtBoldEnd << Mpd.NumberOfArtists() << '\n';
-	*w << fmtBold << U("Number of albums: ") << fmtBoldEnd << Mpd.NumberOfAlbums() << '\n';
-	*w << fmtBold << U("Number of songs: ") << fmtBoldEnd << Mpd.NumberOfSongs() << '\n';
+	*w << fmtBold << U("Artist names: ") << fmtBoldEnd << Mpd.NumberOfArtists() << '\n';
+	*w << fmtBold << U("Album names: ") << fmtBoldEnd << Mpd.NumberOfAlbums() << '\n';
+	*w << fmtBold << U("Songs in database: ") << fmtBoldEnd << Mpd.NumberOfSongs() << '\n';
 	*w << '\n';
 	*w << fmtBold << U("Last DB update: ") << fmtBoldEnd << Timestamp(Mpd.DBUpdateTime()) << '\n';
 	*w << '\n';