Event's source is not always defined in from_abstract_event

Support was added for assigning an organization to an event from the
event's source, but some tests do not include a source.  All known
scenarios in ActivateHub for converting abstract events to events do
provide a source; however, rather than changing the tests and increase
incompatibilities with upstream calagator at this point, it makes sense
to assume source is optional.
Allow setting Google API keys via an environment variable

  $> export GOOGLE_API_KEY=mycustomapikey
Allow setting Google API keys via an environment variable

  $> export GOOGLE_API_KEY=mycustomapikey