Multiple Upload - code review

1. halt uploading of files on first error, and return the data and the errors
2. try uploading all and then return the data and the errors
3. don't upload anything if an error was encountered.

What do you think?

Good job @Avenirer ! I'll wait to see these 3 functionalities you said too, I think this will make it more robust. I 'll also try to do the same thing in my extension too, and update my code.