WIP 0090 - Add skills, Prologue Scene, And Numerous bug fixes

I've fixed a lot of things internally, but there's nothing much to show for it.
I'm adding a few skills. One is a drone that follows the character and fires guns at enemies. And one is a skill that creates a magnetic field that causes damage in random places. I also fixed a bug with the pulse bomb so that it could effectively annihilate enemies.

I created a simple prologue scene to create a cushion for the loading scene. For now, it contains simple story lines that aren't very decorated, but I'll try to make them nicer later.

Besides that, I spent a lot of time fixing miscellaneous game bugs. I also fixed the part where enemies sometimes don't appear. And I also fixed the part where the bullet effect doesn't appear when shooting a machine gun.