ADX-1046 Persist validation metadata

[jonathansberry]

Description

This PR adds two hidden inputs to the end of the resource edit form, one for validation_status and the other for validation_timestamp. This ensures that the metadata is persisted when the resource is updated through the UI.

At present, if metadata is edited without uploading a new file, the validation metadata is lost.

My primary concern about this PR is that it requires us to update the order which plugins are loaded. THis is because validation needs to be able to extend scheming templates, in order to keep this change in validation.

It could alternatively be moved to ckanext-unaids - this doesn't make as much logical sense to me, since the change is strictly scoped to only the validation work, but I can see that it may appear safer and therefore be a preferable option. Happy to hear what @tomeksabala and make the change as he sees fit.

Checklist

Put an x in the boxes that apply to this pull request (you can also fill these out after opening the pull request).
You may not need to check all boxes.

• The Jira ticket for this issue has been updated to "Ready to Review" or equivalent.
• I have developed these changes in discussion with the appropriate project manager.
• My code follows the general Fjelltopp documentation (see Confluence).
• I have made corresponding changes to the Fjelltopp documentation (see Confluence).
• I have rebased this branch with master.
• New dependency changes have been committed.
• I have added automated tests that prove my fix is effective or that my feature works.
• New and existing tests pass locally with my changes.
• My changes generate no new warnings.
• I have performed a self-review of my own code.
• I have assigned at least one reviewer.

[jonathansberry]

Upon reflection, I've closed this PR in favour of including the feature in ckanext-unaids. We want to be minimal in the way we extend validation extension, so we can easily pull from upstream. I think this problem is also specifically related to the way we are using the extension. Furthermore, it is far safer to avoid switching the order of loading extensions - we don't risk incurring cascading issues elsewhere.