SOLIDPOD: add confirm popup when user revoking own access to external file

[jesscmoore]

Description

Now that we've given access to GrantPermissionUI() for recipients with control access, the GrantPermissionUI() allows a recipient to be able to revoke the recipient's own access to a file. As the delete permission button shows on all recipients except the owner.

In practice a recipient should be able to say they no longer want to access an external file by revoking their own access. They are more likely to want to delete their access to an external file, than deleting the external file from the owner's Pod.

E.g. here is karen-reep's list of externally owned files:

if they click on Bird Sightings, to see who can access it, the permission table shows that they can press the delete button to revoke their own access to the file.

Why

I no longer want to use or have access to a file owned by another user. This could be because I no longer have a requirement/desire to access it, or because access has conditions/changed conditions of access in the permissions, which I no longer agree to.

Closing Criteria

Checklist for closing the issue:

• No errors from make prep
• All tests pass make qtest
• A popup appears asking me to confirm that I want to revoke access when I am revoking my access to an externally owned file