Fixed a bug with the Shield

Fixed a bug that caused the shield to be depleted whenever you took
damage, even if the shields were off.

Changed "if (shieldOn = true)"  to "if (shieldOn)"
Added shield and inventory.

Shield now has a texutre when you turn it on. Added a shield class. (may
have to change this later) Added a very beta inventory screen. Don't worry
guys I know it's hideous. Just trying to go with the blue and gold! XD
Just following orders after all. Still need to add buttons to the
inventory, but I'm going to bed.