New level selector, new game-end logic

New Game Selection screen has been added. The planets have been created with this great tool:

https://deep-fold.itch.io/pixel-planet-generator

Also the game mechanics is changed. At the end of the game, above certain score you can finish the level by pusing the Nuke button. You freeze your score but do not risk to loose. 

Some SFX and GFX update made as well on this weekend.

 Playable browser version has just been also updated.