artistname -> artist_name
Merge pull request #77 from germanstudent/dev

fix jingle deletion: artistname -> artist_name
fix for empty episodes array causing shift method to fail

fixes #78
expired cache and a failing fetch_json can cause episodes to be empty. in this case return the old cache state.
using old cache more elegant
more robust external api caching for all external api calls
fix problem with bad cache values for listeners count
Merge branch 'tmp' into dev