Automatically Log Crash Dumps

When a crash dump is detected, it would be really handy to automatically MAVFTP the crash dump, hwdef, parameters, and messages and put them into the documents folder.

That way, if someone gets bad advice to just reflash to "fix" the prearm warning, they'll still have all the relevant information to send to a dev.

We should add a pop-up explaining what this is and why they should report it, and how (maybe even a report-error form).

If there's a way to keep from redownloading the same crash dump every time they connect, that would be nice, but not totally necessary.

Normally, I'd open a PR instead of an issue, but I won't have time to get to this for a bit, so leaving this here if anyone wants to beat me to it.

No file, test, or entry point is named. Start by locating the existing crash-dump detection, MAVFTP transfer, and document-folder handling, then trace how Mission Planner shows pop-ups. Done means crash dumps and the listed diagnostic data are saved without repeated downloads and users are clearly told how to report them.

Written by the indexing model from the issue text.