positionroam: move to GPS Assisted stabi modes

also tidyup with use of PathDesired to store timeout.
And move timeout code to pathfollower
positionroam: simplified state machine and pathfollowr

Also now detecting 90% achievement of vector and then entering position hold.
positionroam: removed thrust mode idea that didn't work
assistedcontrol: multiple updates

1. plan_setup_assistedcontrol now manages a 3D brake vector
2. New interaction between pitch roll and throttle and mode changes.
3. New parameters
4. Feature name change
assistance control: updated xmls
assistedcontrol: fix throttle change override during braking
assistedcontrol: rework pathfollower

1. pathfollower tracking and detection of when to change state to hold from brake
2. control manual vs auto throttle
3. Change of state names
assistedcontrol: Support braking for positionhold flight mode
assistedcontrol: compile errors on other platforms

Add increasing "neutral" range for throttle centering before allowed to exit hold into primary mode.