Ignore failing track preview test

- This is failing due to a missing XML declaration.  The API is being fixed
  to reinstate it.
Merge pull request #94 from raoulmillais/ignore-track-stream-test

Ignore failing track preview test
Added endpoint for basket/applyvoucher
( http://api.7digital.com/1.2/static/documentation/7digitalpublicapi.html#basket/applyVoucher )
can't do integration tests without a supply of valid voucher codes, so will test in a client (the website)
Merge pull request #95 from AnthonySteele/ApplyVoucherEndpoint

Added endpoint for basket/applyvoucher
requires the [OAuthSigned] attribute on "basket/applyvoucher"
Needed on this endpoint in order to work.
Merge pull request #96 from AnthonySteele/ApplyVoucherEndpoint

requires the [OAuthSigned] attribute on "basket/applyvoucher"
According to the docs, the 'user/purchase/basket' endpoint does HasBasketParameter
Merge pull request #97 from AnthonySteele/ApplyVoucherEndpoint

According to the docs, the 'user/purchase/basket' endpoint does HasBasketParameter