Player health

[rafaelgonzalez]

• Player starts with a certain amount of health, dies when health reaches 0.
• Enemies touching the player deplete its health instead of instantly killing.
• Enemies touching the player slow the character down. #10
• Health bar is on the top right corner.
• Color red on grey

[LaurieTrichet]

updated description

[rafaelgonzalez]

Done in #40