Week 3 / Object-Oriented Sets assignment

Raw unzip from https://spark-public.s3.amazonaws.com/progfun/assignments/objsets.zip
Implement filter and filterAcc
Implement union
Implement mostRetweeted
Implement descendingByRetweet
Implement googleTweets, appleTweets and trending

First submission - 8.5/10
Add printList helper & isSorted tests
Fix bug in mostRetweetedAcc

Second submission 10/10 !