Add code to support adding handicap icon to scoreboard

Add code to support adding handicap icon to scoreboard

Currently it's disabled with an if (false), since handicap isn't yet networked to the client.
- This commit will be followed up by networking handicap to the client and enabling showing the icon.
Added handicap icon, based on https://commons.wikimedia.org/wiki/File:Wheelchair_symbol.svg,
... modified with Inkscape to be more consistent with other HUD icons like mediasource's gfx/luma/gfx/scoreboard/player_ready.svg
- Resized to be 32x32 with 3px padding around all edges (and thus made it be "square").
- Made the lines thicker, and extended the foot-rest.
- Increased the size of the gap between the frame and the wheel.
- Removed the arm-rest.
- Mostly properly aligned the head to the right.
Scoreboard changes:
- Now player_ready and playercolors can be shown simultaneously, side-by-side.
- Support for this was added with sbt_field_icon_extra*.
In future it may be worthwhile considering making the extra icons align right, I think that would look better.