Resume on crash ability / keep track of progress

[ramotswa]

This is probably more a feature request than anything else;

It would be great to be able to pick up from where the loader left off in the case of a server disconnect / crash etc. I guess if the .sql files don't get deleted you could do an if exists on those, or keep track of what is being processed in a txt file...
Biggest issue I can see is that the subprocesses that are being called can't really raise an error if they fail, so we can't know if the ogr2ogr (for instance) completed successfully or not.

Happy to have a chat how this might be done and potentially contribute.

Cheers