ship removal when damage

hud.js:
- Removed playerLives variable and used the pre-existing playerHealth
variable. The HUD will use this variable to determine how many ships to
make in the HUD.
- added the removePlayerLife() function. This gets called everytime the
player takes damage.

player.js:
- added resetPlayerScore function and resetPlayerHealthNum variable.

gameModeState.js:
- added a check to say gameOver=true is the playerHealth is 0. game will
return to start state when player's health is 0