Nonlinear joystick

Code to add nonlinear response to joystick, so that it's less jumpy at the centre while still allowing the full range if pushed to extremes. I've put four options to play with in the code, selected by setting STICK_NONLINEAR_OPTION in OOJoystickManager.h:

Option 0 is equivalent to current setting.
Option 1 is as is in normal mode but makes precision mode nonlinear
Option 2 makes normal mode nonlinear while leaving precision mode as is
Option 3 makes both nonlinear with precision mode more precise around the centre.

I've been told there's some work being done to make the deadzone configurable - I've put the deadzone code in OOJoystickManager and added deadZone and setDeadZone methods to get and set the deadzone.

See thread on BB here:  http://aegidian.org/bb/viewtopic.php?f=6&t=15770