Star Feature

[jeremysmithco]

Allow Samples to be starred (favorited) by users.

• [ ] Add Star model, associated with sample and user
• [ ] Add star count (counter cache) to Sample
• [ ] Add functionality to create and remove Star
• [ ] Add star count to Sample card
• [ ] Allow sorting of Sample views by star count and created date
• [ ] Add view under user profile to show user's list of starred samples