Add error logging for batch exports

[maxclevenson]

This tool is incredibly helpful, thanks for sharing it!

When doing a batch export, the sequence of error dialogues when an asset exists can be a bit of a pain, especially on larger projects. It'd be great to either have a list of the errors that happened during the export in the app's interface, or just log it to an errors.txt file in the root of the output directory.

[asystat]

You are right. Rhere should be a "replace all" checkbox, and error list. When I have some time I'll add it ;-)