Added comment in qt_gui.py that gs is a GeneralSetting.

Leo build: 20140917061246
Continuing to improve and clean leoSettings.leo:
- Removed all unused settings.
- Improved introductory remarks.
- Added a node called "Appearance (change these first)"
- Improved the comments for the two children of the "Appearance" node.

Leo build: 20140917061448