Remove global override of Math.random #27

Early on, I decided to use seedrandom's { global: true } option. It was a silly decision in retrospect.

The big change here is that seedrandom should be internal to terra and not pollute Math.random().

Following this thread, seeded RNG should really be handled more granularly anyway. Initial thoughts:

1. Each terrarium is given a unique ID
2. This ID is used to seed the terrarium's RNG

That way, a terrarium recipe and ID are all you need to perfectly reproduce a simulation. It'll no-longer be bound to other uses of random() on the page.

Thanks @benswinden for the heads up! 👍