BBCIE: Fix missing .mp4 formats on news sites

BBCIE: Fix missing .mp4 formats on news sites

Prior to merge BBCNewsIE from pr #6026 was rewritten into BBCIE in 9afa177. Support was added for non-news
sites (/travel, /sports), however support for the news mediaselector was removed to support these sites.
This removed support for .mp4.

    pr #6026 ( news site, news mediaseletor : http://open.live.bbc.co.uk/mediaselector/4/mtis/stream/ )
    format code                                          extension  resolution note
    journalism_nonuk_stream_h264_flv_200_akamai          flv        400x224    h264@ 176k, 1001.77KiB
    journalism_nonuk_stream_h264_flv_400_akamai          flv        400x224    h264@ 512k, 2.85MiB
    journalism_nonuk_stream_h264_flv_med_akamai          flv        640x360    h264@ 800k, 4.43MiB
    journalism_nonuk_stream_h264_flv_hi_akamai           flv        688x384    h264@1500k, 8.34MiB
    journalism_world_stream_h264_http_200_sis_news_http  mp4        400x224    h264@ 176k, 1001.77KiB
    journalism_world_stream_h264_http_400_sis_news_http  mp4        400x224    h264@ 512k, 2.85MiB
    journalism_world_stream_h264_http_hi_sis_news_http   mp4        688x384    h264@1500k, 8.34MiB (best)

    # 9afa177 ( same url, non-news mediaselector: http://open.live.bbc.co.uk/mediaselector/5/select/version/2.0/mediaset/journalism-pc/vpid/ )
    format code                                  extension  resolution note
    journalism_nonuk_stream_h264_flv_lo_akamai   flv        384x216    h264@ 496k, 2.76MiB
    journalism_nonuk_stream_h264_flv_med_akamai  flv        640x360    h264@ 800k, 4.43MiB
    journalism_nonuk_stream_h264_flv_hi_akamai   flv        688x384    h264@1500k, 8.34MiB (best)

This change corrects the above, by trying /mediaselector/5 if /mediaselector/4 fails.