plugins.bbciplayer: fix for page formatting changes and login
plugins.bbciplayer: fix for page formatting changes and login

The beeb now enforces logins for watching iPlayer, logins are now
enforced by the plugin.

back-to/streamlink,chhe/streamlink,streamlink/streamlink,javiercantero/streamlink,gravyboat/streamlink,bastimeyer/streamlink,melmorabity/streamlink,beardypig/streamlink,wlerin/streamlink,chhe/streamlink,bastimeyer/streamlink,streamlink/streamlink,beardypig/streamlink,javiercantero/streamlink,wlerin/streamlink,melmorabity/streamlink,back-to/streamlink,gravyboat/streamlink