cryptui: Add a partial implementation of CryptUIWizImport.

[Juan Lang]

> It may not persist but I could import the certificate fine on Wine.
> Is there an alternative for the root store? What's involved in making
> the root store read-write?

You haven't convinced me that Windows does indeed import the
certificate to the root store in all cases.  Making the root store
read-write isn't the right answer.  Please write more tests first.
--Juan