FoodRecommender v2.0

[johnding1996]

• [x] Propose the changes and review
• [x] Implement the FoodRecommender v2.0
• [x] Add more unittests since it's more complicated
• [ ] Integration test and merge by PR

[johnding1996]

Proposed changes at #85. Please review this.

[johnding1996]

@thomaszhouan Feature 11 PR ready, please review it #98. Deployed to test0.

[johnding1996]

The new FoodRecommender is ready! issue closed.