Build a crash report now, for the user to look at and then send

fppd builds a full report (settings, configuration and logs, level 3) named like a crash report with a -manual suffix, and keeps it in the crashes folder (two manual reports at most). Nothing is sent: the user can download it from GET /api/file/Crashes/<File> to see what it holds, then send it with POST /api/crashes/upload/<File>, which needs their consent. client names the calling app in fppd.log. A build takes seconds on a fast player and can take a few minutes on a Pi Zero or BeagleBone. One build a minute, counted from the start of the last one. Error Codes: bad-request, busy, rate-limited, build-failed, unavailable.