Mechanical stuff we need for the Insomnia demo build

[FireWaterGasoline]

1) GB time limit; 2) planets have mass - more mass harder to change speed; 3) GB stops at sun; 4) planet hold time limit.

We need these bad boys to have the game playable and enjoyable.

[kirijiri]

3 done

[kirijiri]

1 done -> no effect yet