Find and remove all study-specific code from WebScience

[akohlbre]

• AggregateStatistics should be in the study code directory
• UserSurvey.js is being rewritten, but the current version has some hardcoded study-specific values

[jonathanmayer]

I removed AggregateStatistics from WebScience: https://github.com/mozilla-rally/web-science/commit/92ee41cc928ab1018c04730a5a58f719f1ea7b63

The userSurvey issue is on the web-science repo: https://github.com/mozilla-rally/web-science/issues/10