Record MAVLink telemetry in a .tlog file

[ES-Alexander]

This is generally expected functionality for control station software, and provides some data security in the case of a lost vehicle.

Not sure how hard it is to continuously write to a file from a web-app, but hopefully it’s possible and not too problematic.

[rafaellehmkuhl]

We don't have access to the raw MAVLink messages right now, so we would have to save a JSON file with messages coming from mavlink2rest and them parse them to raw messages.

I suggested patrick that we add support for saving and downloading .tlog files in mavlink2rest itself, as it would be relatively easy and would provide this feature universally to others using it. Issue opened here.

[ES-Alexander]

The priority is recording the input and output data in some form, even if that means we have to create a custom format/parser for it (.tlog just happens to be how it's done currently in other control station softwares, so could be nice for user familiarity).

#546 will likely help with this.