Changing menu screens

[andy5995]

The 3d menus and backgrounds are mostly recycled from MegaGlest. ZetaGlest is a colorful game. I think the menus could look sharper and brighter.

I'm not a designer, but if anyone would like to submit some samples, they'll be reviewed and discussed here. Any approved changes will be merged through a PR.

Most of the files for this are in https://github.com/ZetaGlest/zetaglest-data/tree/develop/data/core/menu/main_model

Since the menu background are animated 3d representations, to test your changes or to see a full picture of how things look now, you would need to run the game. Or perhaps just viewing the models existing in the repo would be sufficient for some modellers.