Create a Universe class

[chrisgrounds]

We need some way to represent the entirety of each level, which we could do with a class. This class would want to basically store values representing the start and end of the level. Could make them random values too, so each level varies in length.

We'll also want the Floor class to inherit from this class, so we don't have to redefine the length of the level.

[chrisgrounds]

@sjoedwards has made a super cool class that does this:

https://github.com/CoilBrew/sidescroller/blob/master/src/Universe.py

So going to close the issue.