Docgenerator loaddb/freezedb safety

[mscuthbert]

Moved from
w3c/mnx#350

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Since the sqllite file isn't committed to disk and doesn't change as branches change, but the m[usic|n]x(ml)?.json file does change with each branch change, I've found myself needing to be paranoid about whether I'm overwriting an older version of .json or of .sqllite with my loaddb/freezedb commands.

I wanted to propose that the spec.manangement.commands.freezedb/loaddb files check the timestamp of the .json file vs. the .sqllite file, and if the one being overridden is newer than the one being written from, that there would be a prompt asking for permission before doing so.

I was going to implement this on my own, but I realized quickly that I've never used Django with an sqllite db, so I couldn't figure out how to get the modified time of the database. If you agree that this would be useful, you can just send me the code to find the sqllite file (from within a management command) and I can probably write the rest quite easily.

Thanks!