404 error when uploading a file that fails postgres rules

There is a bug in this extension when creating a new resource that contains an invalid structure (e.g. duplicate column names).

After clicking on "Add", the user is directed to a non-existent page (`dataset/dataset-page-name/resource/new`) with a 404 error:

## What should happen
After clicking "Add", if the validation status is not "success":
1. the user should be kept on the add resource page
2. the validation report should be shown at the top of the page, in the same way that it is displayed for updates of existing resources
3. only after the user uploads a valid file should the application redirect to the resource page