Game Theme Reimplementation

The part of the main menu that controls the game theming aspects is implemented with mm_game_theme, in game_theme.lua. If you wish to rebrand the main menu, dealing with the complexity of this implementation can be rather unnecessary if you just want a single background and header that shows up on every tab.

What mm_game_theme does is essentially just abstract away calls to core.set_background, a function which controls background textures, but also header and footer textures. See the entry for it in

* `core.set_background(type,texturepath,[tile],[minsize])`
  * `type`: "background", "overlay", "header" or "footer"
  * `tile`: tile the image instead of scaling (background only)
  * `minsize`: minimum tile size, images are scaled to at least this size prior
   doing tiling (background only)

This is an example of a minimal reimplementation (from Voxelmanip Classic) that shows a static, untiled background and a header from the base textures directory in the main menu:

core.set_background('header', defaulttexturedir .. "menu_header.png")
core.set_background('background', defaulttexturedir .. "menu_bg.png")

This would be put in the init_globals() function in place of calls to mm_game_theme.