Edit a verification request

[tortila]

This PR aims to enable editing of submitted verification requests by their authors, using the same multi-step wizard form.

Scope of changes:

• New URL path to the edit view: /requests/{id}/edit which is only accessible for admins and authors, and only when the request is open. We re-use the same WizardView but this time pass an instance_dict as an argument, which contains model instances as expected by consecutive steps.
• All forms used by the wizard are now either ModelForm or ModelFormSets. This allows to inject either an instance of queryset with existing objects and delegate handling the updating/deletion of objects to Django magic.
• Status "Open" now renamed to "More info required", added a relevant migration.
• New button on the detail page of a verification request: "Update this request" will be visible to request's author and admins when the request has status "More info required". The button redirects to the edit view.
• Some workarounds for MultiModelForms and ConvenientFormSets for the whole machinery to work properly (all workarounds documented in the code with examples).
• New action added to the admin panel: requesting more information about a ProviderRequest object will mark its status to OPEN.
• Clean up models for representing consent (last step of the verification request form): now consent fields are a part of the ProviderRequest model and not a separate one. Added a relevant migration and changed the model forms.
• Small change in the CSS: added a rule to always mark elements with attribute "hidden" as display :none. This is a workaround so that evidence rows can be deleted, this didn't work before because the flexbox overrides the "hidden" attribute behavior.
• Added some tests, including test_editing_pr_updates_original_submission which covers an end-to-end journey of updating a verification requests.

Out of scope:

• attaching notes/comments by staff to opened verification requests,
• automatic email communication with the author in case a verification request is re-opened.

After merging:
Remember to run the migrations!

[gitpod-io]

[mrchrisadams]

hi @tortila thanks for taking me through this on the call just now - I feel like I have a good understanding of the changes now, and the last few bits before we merge it in. Have a nice week away :)

[mrchrisadams]

Oliwia and I reviewed this code synchronously on a video call, and again in person. I'm happy to merge this in.