Insights: Use collections.defaultdict

A lot of code right now is in the pattern of:

if foo in bar:
    bar[foo] += 1
else:
    bar[foo] = 1

This can easily be simplified with defaultdict, which was specifically
designed for this very purpose.
Merge branch 'master' into defaultdict

Conflicts:
	helpers/insights_helper.py
Merge pull request #974 from legoktm/defaultdict

Insights: Use collections.defaultdict