Draft: kcms/users: Totally new unseen before UI for deleting users

Deleting users is a scary process. It doesn't help that currently all it takes is a double-misclick to remove a user from the system altogether with all their files: the confirmation menu appears right on top of the "Delete User…" button, with the most dangerous option showing up straight under your cursor.

Hence, let's add some safety straps: full-sized modal dialogs, attention-drawing blurry background, extra step that require explicit user consent, and of course some unskippable timers.

Totally not inspired by a certain gaeming platform. No way.

Note: Draft status is because this patch incorporates too much in one chunk. It should be split and polished. Also actual deletion of users is disabled, and replaced by a fake (random) status response, for convenience of testers. So feel free to check it out, and don't worry about your data!

Requires these icons: frameworks/breeze-icons!247