BBC Parser: Support choosing version of programme when given parent URL

[GalvatronJB]

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Description of your issue, suggested solution and other information

For programmes that have multiple available versions (i.e. original, podcast, iPlayer), the BBC parser when given a parent URL (programmes/[vpid]) only downloads the default available version of the programme, whatever that may be.

If a programme has more than 1 version available, the user should be able to specify which version they would like to be downloaded.