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.
Update readme setup section
Merge pull request #987 from josephbisch/readme-setup

Update readme setup section
Allow trailing slash in URLs
Merge pull request #988 from josephbisch/redirect-routes

Allow trailing slash in URLs
Update links to point to new Github repo
fixed binning in score distribution insight
suggested changes
Merge pull request #994 from brandondean/github-address

Update links to point to new Github repo
Update Travis link in README
...
Merge pull request #995 from lemiant/master

Fix score distribution insight calculation
event stats in API. replaces #984.
documentation for api event stats
Merge branch 'master' into defaultdict

Conflicts:
	helpers/insights_helper.py
api event stats test case
Merge pull request #974 from legoktm/defaultdict

Insights: Use collections.defaultdict
Return full event model for event list request
Merge pull request #997 from the-blue-alliance/api-stats

Api event stats
Merge pull request #998 from brandondean/event-list-updates

Return full event models for event list API request