Update MavFTP code, add MavFTPfs example/tool

[Williangalvani]

This mounts mavftp as a virtual filesystem, which allows for more "human" interfacing with it.

There are caveats. It is obviously slower than doing things on your own machine. but this does allow interfacing using any filebrowser, for instance.

So far the filesystem is mounted as read-only. as there's no mavftp interface to write to a sector of a file, we'd have to create an abstraction layer that caches the whole file...

Screencast from 2024-09-17 12-21-47.webm