front: Implemented virtual gamepad scaling
I added two new optional parameters to the INFO section of pad.ini for virtual gamepad layouts.  These parameters specify the intended width in both pixels and inches.  The auto-scaling uses these to adjust image sizes to the target device.  This is still pretty rough, but the basic functionality is in place.  The default pixelWidth and inchWidth for the gamepad layouts will likely need to be adjusted (I based the numbers off of my old Droid X, just to make sure the auto-scaling was working).  I haven't implemented separate logic for Tablets or portrait modes yet.