Fix Platform Y Calculation

Fixes a bug in platform y calculation for platforms other than the
floor.
Add Function to Generate Random Platforms Tiers
Move Camera Back to Positive Coordinates

HaxeFlixel's already-questionable physics completely loses its mind if
coordinates go negative.
Make Floor Visible

This part of the calculation was erroneously removed when I moved the
game space back to positive coordinates.
Improve Platform Generation

The previous generator was getting unwieldy and this one is more
aesthetically pleasing.