CC-5709: Airtime Analyzer

* Catch exceptions related to unpickling the HTTP request queue
Merge branch 'cc-5709-airtime-analyzer' of github.com:sourcefabric/Airtime into cc-5709-airtime-analyzer
CC-5709: Airtime Analyzer

* Fixed some unit tests that broken when I dropped python-magic in
  favour of mutagen for MIME type detection