Shield texture not disappearing

Shield texture was not disappearing even when it's health was equal or
below 0
Background level 3

Background wasn't changing for level 3 - corrected by adding in the
relevant line of code that loads the specific texture for level 3
Laser Invisible

The lasers being shot were still staying loaded in game memory even when
going off screen - this was fixed by adding in the relevant line of code
to make the game smoother and delete any memory being accessed by
needless code