Adding new enemy and changes to some scripts

[labelled]

Hi there,

I made a few changes to some of your scripts as outlined below as I wanted to create a new enemy for your game. This new enemy I had in mind is similar to the idea of the enemies you wanted to create in your game. I went with a simple design and a simple beam image as when the enemy shoots out the beam and hits the player. I didn't want to use too much of the behaviours since I wanted this enemy just to shoot and orbit the player. It has a bigger health bar and score based system since it is not in all of the waves that I have seen in your wave list. However please let me know if this is acceptable from the changes that I have made.

Thanks.

[drhayes]

Oh my gosh! I just now noticed that I have a PR on this repo. Let me know if you still want me to look at this!