Joystick tweaks. (DO NOT MERGE)

Ensure that the joystick can always reach -1.0, 0.0 and 1.0 positions
even when noise filtering is applied.  (Bug: 3514510)

Add support for a few more standard axes.

Add additional mapping modes for axes.
Some axes are inverted from standard interpretation
or are actually intended to be split into two distict axes
such as left/right trigger controls or accelerator/brake.

Add key layout file for a G25 racing wheel and XBox 360 controller
to tweak behavior.  They work fine without them but the axis mappings
are not ideal.

Change-Id: I0fddd90309af4dc14d35f34fe99ed6e521c0b7c7