New insight: Twitter age

Looks at your Twitter join date and gives you a colorful first-run insight.
closes #1916, closes #1934
Support for images in posts in insight email

Closes #1942
Twitter Birthday Insight

Each year on your anniversary of joining twitter, gives you an insight.
Shows people you follow that joined just before and after you.
Added getFollowersJoinedInTimeFrame and countTotalFriendsJoinedAfterDate to FollowDAO