[fb-impact-insights] Removed unused stuff, PEP8 and structure improvements
[fb-impact-insights] Move common functions to fb_utils.py

- Make accessToken global
[fb-community] Several bugfixes and less verbosity

Catch empty data in get_insight()
It was causing a crash since for some old posts,
for task=post_impressions_paid_unique the "data" json attribute is empty...