Mini Panels for c172

List of files:

./keyboard.xml - same as release key bindings with "s" added to swap panels.
./preferences.xml - same as release preferences.xml with "panel2" added.
./Aircraft/c172/Panels/c172-panel-mini.xml - mini with sacred six, compass, 
	mixture knob, flaps, and control indicators.
./Aircraft/c172/Panels/c172-panel-trans-mini.xml - same mini panel with 
	plexiglass (transparent) background.
./Aircraft/c172/Panels/Textures/panel-mini-bg.rgb - grey background.
./Aircraft/c172/Panels/Textures/panel-trans-mini-bg.rgb - transparent background.


USAGE NOTES:

Hitting "s" will switch between the standard panel and the default.

You may choose other panels for the two that get toggled by changing the
preferences or adding command line parameters.

The property for the panels are:
Normal (Primary) panel: /sim/panel/path=<path to xml file>
Mini (Secondary) panel: /sim/panel2/path=<path to xml file>

The new property is /sim/panel2/path,  it does not need to be a mini panel, you 
can use whatever you want.

For example: to use the grey mini panel change preferences.xml or add this to 
your command line:

runfgfs --prop:/sim/panel2/path=Aircraft/c172/Panels/c172-panel-mini.xml