The "free X" powerups now only appear if you have at least one of the item, and also stop appearing once you have 100

Before, each one multiplied the time between spawns by 0.5
Now, they multiply the time by 0.75, then 0.78, then 0.81,
and so forth

This is needed to make sure that all of the buttons get updated - some will
have stale states, otherwise

The last state of the upgrade buttons are now cached. This ensures that
the classList is perturbed *only* if this would actually change the
appearance, and seems to be far faster than just adding something
to the classList over and over

Since I did not explain deep-freezing in the last commit..it essentially
makes an entire object read-only, meaning that instead of mangling important
data, badly written code will throw an error!

This has broken quite a bit, since many parts of the game expect a scalar instead of
a whole object. I have also been deep freezing constant configuration data and, generally,
trying to make as much immutable as possible