SFTP for files to/from companion computers

#### Issue details
Vehicles with a companion computer require moving various files between the windows PC and the companion computer. Today that is primarily log files and python files. We're using applications such as WinSCP and Filezilla to do this today. Or customized little scripts that use executables and command lines.

It would be great if Mission Planner had an SFTP interface to handle this. It would make Mission Planner even more of a one-stop-shop and really streamline the process. And even better if the configurations were available as presets. The two primary ones these days I think are APsync and Solo's IMX.

Perhaps even some "macro" functions could be baked in? For example, downloading log files from the Solo is the same repeatable process with the same files in the same directories. Probably just like APsync.

#### Version
All

#### Platform
[ X ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
All

#### Hardware type
Companion Computers

#### Logs
N/A

The issue names no files, tests, or entry points. Start by locating Mission Planner's existing companion-computer file-transfer UI and assessing the scope of an SFTP interface, APsync and Solo presets, and repeatable macros; done would require an agreed design covering these requested workflows.

Written by the indexing model from the issue text.