Fixed error when clicking the 'View changes' button on a resource edi…

[achraf-jeday]

Ref https://github.com/NuCivic/wbddh/issues/377

Steps to Reproduce

1. - On any resource, click 'Edit'
2. - Make a change to any field
3. - Click 'View Changes'

A new resource is created with the changes. The original resource is unaltered, and there is no normal 'view changes' dialog.

[janette]

[janette]

1. we loose the file object from the upload field
2. tests should fail, so we need a test for 'view changes'
3. check what happened here: https://github.com/NuCivic/dkan_dataset/pull/276/files
4. Ignore what the image says about buttons, the buttons are the correct resource form buttons.