add "overwrite" option in build_graphs_batch

[rkurchin]

Should default to true, but if false checks if given path already exists in output folder and skips to speed things up, allow finishing an interrupted graph-building

[thazhemadam]

If it skips to speed things up, wouldn't models using this be relatively faster if this were to default to false instead?

[rkurchin]

hahaha yes I did say that backwards, good catch...OBO errors are a real bitch in binary, eh? 😆