UI definitions

UI elements can be both loaded from Lua definitions or created on the fly.

UI styles

Modeled after CSS but using pure lua.

Each UI element has:

• id value, might not be set
• type value, set by type database
• class value, might be set by user
• special modifier (selected, hover, etc)

default = {
  text_color         = { 0.3, 0.3, 0.3, 1.0 },
  background_color   = { 0.0, 0.0, 0.0, 1.0 },
  background_image   = "source:path/name/file.png",
  background_stretch = 
}