Refactor joystick handling

    * Removes Linux-specific joystick handling
    * Adds cross-platform GLUT joystick handling; Caveats:
        - GLUT is not robust to joystick hot plugging like my old Linux-specific code was.  (Fix should be made in the
          GLUT driver and pushed upstream if we really care)
        - Deprecated X11 renderer now can only use keypad joystick
Squashed 'Apple2Mac/DDHidLib/' content from commit e6a9848

git-subtree-dir: Apple2Mac/DDHidLib
git-subtree-split: e6a9848859fc84e689afb85799658f4980651106
Merge commit '7d64531b89057a2beed03af65b8ed6d1e5a1ddce' as 'Apple2Mac/DDHidLib'
Handle joysticks/gamepads on Mac