I fixed three issues with the game:

1) I redid the spacing of the space invaders so there distance from one another (both horizontal and vertical) and their starting locations are all multiples of 16. This fixed the problem of the invaders landing on the earth and overshooting the earth's surface by a few pixels.

2) When the invaders would start on the next level after the player cleared the previous level, sometimes the invaders would move right and sometimes they would move left. This problem was fixed by initializing the space invaders manager at the start of each new level with the value +1 to represent the invaders always starting off moving to the right.

3) I also added a new dimension of difficulty, with the start of each new level, the space invader's positions all start one row closer to the earth.

I also cleaned up some of the code a bit.
Merge branch 'master' of https://github.com/garyfredgiger/SpaceInvadersClone

I am pulling from the remote master since my head version is behind the head of the online repo.