* Deal with missing parameters on Solo

* Fix trigger set

Temporarily disable MAVLink version check as the QGC settings have no effect and it will mess with the upgrade from v1 to v2 and has no real value

Throttle trim must be center throttle

- Cache only supported on PX4. Solo sends param updates at a high rate
to update gimbal values. This was causing the cache to update itself at
too high of a rate, killing performance, especially on iOS.
- Fixed read/write index usage to provide correct progress bar updates

They may show up after parameters ready is signaled. No way around this
since this is a protocol problem. So can’t test secondary component.

- Now responds to request_list using a worker routine to send out
params one at a time
- Support for failure modes for unit testing

Vehicle change: All items removed
Vehicle add: Request sync is not already in progress