change planet scaling

[irapha]

1. Planets are too small.
2. Planet sizes should vary more in low populations
3. there shouls be a standard size for planets with pop1. It should be visually visible that planets of pop < 1 are, in fact, < 1 and it should be clear how close they are to reaching pop 1. (0.2, 0.4, 0.7..... 1)