Add confirmation dialog when blocking or deleting a user

[gtsiolis]

Problem to solve

Currently, when you try to block or delete a user from the Admin Area the action is performed immediately without waiting for any further user confirmation. This can surprize the admin user as well as be more prone to accidental errors.

Proposal

Add a confirmation dialog when an admin user tries to block or delete a user from the admin area /admin.

Designs

For blocking a user:

1. Modal title: Block User
2. Modal body: Are you sure you want to block this user?
3. Modal actions: Cancel, Block User (primary, danger button)

For deleting a user:

1. Modal title: Delete User
2. Modal body: Are you sure you want to delete this user?
3. Modal actions: Cancel, Delete User (primary, danger button)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[gtsiolis]

Still an issue. Adding never-stale label.