fix data_class and set file name in transformer

The data_class option of the ImageType was ignored. 
The transformer lost the original name of the file.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | [yes|no]
| Fixed tickets | n.a.
| License       | MIT
| Doc PR        | n.a.