[CollectionUpload] Manage additional fields on file link

[sescandell]

Currently, in async and sync mode, additional fields are handled on "edit" form.

They should be available:

• on file upload in sync mode
• after file is uploaded on async mode (or before?)

[sescandell]

Fixed with commit https://github.com/symfony2admingenerator/FormExtensions/commit/a87f49dda06c81849cc74daa33f2978d5ebebce9