Support Alternative cbs.com URL Format

Adds support for cbs.com URLs containing "/artist" instead of
"/video". E.g.:
http://www.cbs.com/shows/liveonletterman/artist/221752/st-vincent/
Merge remote-tracking branch 'jterk/cbs-artists'
[cbs] Modernize

Also add threatening skip blocks in there - access is only possible from the US. We may want to find a better geolocation restriction method for tests.