Add Clicks to clicks hash
Add click_id to Click class
Failing test to get all clicks for a given link
Failing test to store a hash of {link_id: x, click_id: y} when link is clicked
Store hash in join table when link is clicked
Modify get_users_links test so it passes a user_id instead of a user. Fail the test.
Database.create_link now takes user_id instead of user. Link stores user_id instead of user.