Jim Wilson:

Jim Wilson:
These changes should preserve previous functionality (with the exception of a
couple bug fixes).

Bugs fixed:
- AP no longer resets the error accumulator when switching altitude modes or
just closing the autopilot GUI.  It will not be necessary to collect the barf
bags after selecting a new altitude anymore.  Makes things much smoother.
- climb_rate calculation in the altitude hold mode included a factor that made
sense for the c172.  It is now scaled according to the configuration's target
climb rate.

Additions:
Autothrottle (supports speed control only) is more configurable and accurate.
VerticalSpeed mode added (automatically arms to altitude if flown toward
altitude setting).
Exposed various properties, added new lock properties.