[Dropzone] Support for multiple files upload

[andersmateusz]

As of my knowledge dropzone does not accept multiple files upload and despite nice try of implementing this feature #7 issue was closed. I think multiple file upload is essential for dropzone. I am right that this feature is still not implemented?

[weaverryan]

Correct! We just need someone to help carry this forward and think about how it should look and work. I'm going to close - as the issue #7 is still open (the corresponding PR #512 was closed), but yes, still needed 👍

[andersmateusz]

@weaverryan Sure I will try to implement this