CLC-3864: Webcasts: change link to iTunes U to "Also available at <link> iTunes U</link>"
https://jira.ets.berkeley.edu/jira/browse/CLC-3864
Merge pull request #2654 from christianv/CLC-3864b

CLC-3864: Webcasts: change link to iTunes U to "Also available at <link> iTunes U</link>"