Allow passing UID to importer

[reduz]

This helps, for importers spitting out new resources to the res:// filesystem to actually hash them to generate deterministic UIDs.

This PR also fixes the determinism for translations.

[fire]

Curious, I need to investigate if generates a deterministic uid or merely doesn't repeat because it's from one generator.

Also the problems with duplicate uids.

[reduz]

@fire it should be fine, it uses the generator for the base file, then hashes depending on the generated file, so it pretty much is unique.

[Repiteo]

Thanks!