cloud storage branch (for the last time)
* Backported all the bugfixes from cc-5709-airtime-analyzer-cloud-storage
* Backported missing FileStorageBackend.php
* Fixed CC-6001: Track titles and artist names with slashes break audio preview
* Refactored all the MediaController code, pulling out the logic into MediaService
* Fixed an API key leak to guests in the Media API
* Made this branch work without cloud_storage.conf (defaults to file storage)
* Made ApiController's getMediaAction use the MediaService code