Add settings for vertical wheel display (XCenter, XSelected, OffsetAngle)

[Billiam]

I was curious about having a vertical wheel display, and this seemed like a reasonable set of changes.

New options

• XCenter: A horizontal wheel center, matching YCenter
• XSelected: Horizontal position of the selected wheel image, matching YSelected
• OffsetAngle: The currently selected game's rotational position on the wheel in radians

Other changes:

• Doc and comment updates where appropriate
• Handful of space-indented lines in Playfield.cpp converted to tabs for consistency
• Typo in DefaultSettings.txt

I think this will work best with wheel images that are all the same size/aspect ratio.

Future improvements could include additional control over the info box position and size, and direct controls or limits on size of the currently selected wheel image.