ABM.Model constructor accepts a single world object parameter

I moved the old `setWorld` function to `setWorldDeprecated`. You can still pass in a bunch of arguments like before, but I changed the example models to use a world object instead. Omitting the `div` option is the same as setting `isHeadless` to true.

In the future, instead of specifying `minX`, `maxX`, etc., it might be better to specify something like `xExtent = [minX, maxX]`. Also might want to rename the `size` parameter to `patchSize`.