* fix(recording): fetch events also for available broadcasts

Only "persistent" broadcasts were being fetched using the
YouTube API. Fetching "all" will get persistent broadcasts
and events. If events use a custom encoder then the stream
key can be obtained. If google hangouts is used for the event
then a stream key will not be obtainable; in those cases
input empty string as the stream key.

* squash: fix typos, reword comments, use object for preventing duplicate broadcasts