DeletionModal react component (move from assets-admin to admin)

[Zauberfisch]

For a CMS module I'm building I need a "confirm deletion" modal.
There actually is an existing component DeletionModal.js and is very generic (body and buttons are props), but it's part of assets-admin and not exported for use in other modules.

I think a confirm popup (deletion or other) would be a useful component to have. So I'd like to propose just moving it into admin and make it available to all modules.
(Only minor change: title is static and needs to be made a prop)