Change a lot to supply arbitrary input for cell size.

Signed-off-by: spacewander <spacewanderlzx@gmail.com>
At the beginning, I just wanted to change the limit of universeSize, however I found myself in the place with lots of code changed finally.
This and next week, I am engaged in the enrollment of my associations, and there is no time to spend on programming. Thus, I will quit improving this project. Time to back for my homework.