Improve configuration system

[historic_bruno]

• Unify command line options, config files, overrides, and console/GUI
• Organize config files, possibly like ​INI files
• Support overriding user config, preventing other based on system capabilities, etc. - important for graphics config
• Allow e.g. hotkey sets
• Create decent API for scripts to access and modify config
• Some settings might take precedence over others, e.g. high/medium/low graphics settings vs. shadow map detail, filtering, etc.
• Better detection of GPU/driver capability, see also #145
• Support mod config files
  • Examples: a mod that overrides default camera settings, or a mod that defines its own completely new settings

See IRC discussion on ​2013-01-03 around 17:41. Some thoughts from Philip ​here.