GCS/Input: make throttle stick visualization realistic

Because of the way we map the majority of the throttle range to
[0,1] in the UAVO, the wizard normally shows the throttle quickly
jumping up to the mid position and then moving more slowly. This
has confused some of the users. Now it should match the physical
stick position.
Merge pull request #1318 from peabody124/input_accurate

GCS/Input: make throttle stick visualization realistic