CLC-3682 Don't cache AllPlaylists so long

https://jira.ets.berkeley.edu/jira/browse/CLC-3682

Cache the list of all playlists at default (35 minutes) so that any revoked webcasts will get cleared from our site faster. Youtube lists are still cached for 24 hours, but this is fine since the Youtube list is derived from the playlists found in AllPlaylists.