Add support for ArduRover MockLink

Support STATUSTEXT_LONG

16 RC channels

Support parameters from multiple components

* Flight modes still not implemented. Waiting on message change.
* Also includes various cauterization of UI things which should not be
available on high latency link.

Fix merge issues

This reverts commit 52160d80.

Pulling mavlink with a reversal for the CAMERA_IMAGE_CAPTURED message. It's now back as it was so it won't break existing code.
The pull also brought changes to the GPS_RAW_INT message. Only MockLink uses. I entered zeros for all new fields.

Prevent shutdown ordering crashes

_finalize methods need information which is not available if all you
have is a mavlink_message_t

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