Create happiness bar

[jacquelinehuang]

Create health bar functionality above pet so we can monitor how we are taking care of the pet

[kariwhiteside]

Mentor approved!

[chenyinluo]

will the health bar different according to the kind or other element of the pet?

[jxu495]

2/13: Changed the issue to be a happiness bar since the feeding mechanic might be better suited to deal with the health bar.

[jxu495]

Acceptance Criteria:

• Have a visible bar element that keeps track of pet's overall health.
• The health bar should go down over time.
• Playing with the pet should restore health (the ball)