EmulatorGLView posts an NSNotification rather than calls API method(s)

    - Joystick connectivity polling is a consumer
key handling improvements

    - keyboard joystick axes handled separately
    - discriminate more classic-interface-only codepaths
Pause emulation if prefs or disks window becomes key
Joystick controller fixes

    - only poll for joystick connectivity once per second
    - if keypad joystick enabled, pump the handler
Adds a joystick calibration routine to preferences window

    - TODO : use common code paths for key handling