Use readonly edit controls in some Windows dialogs.

Use readonly edit controls in some Windows dialogs.

This makes the About and Licence boxes copy-and-pasteable, similarly
to what I've just done on Unix.

(But unlike on the Unix side, here I haven't touched the host key
prompt dialog, because that's a standard Windows MessageBox and not
easy to mess around with. Plus, in any case, you can already hit ^C to
copy the whole text out of a MessageBox. Same goes for the PGP
fingerprints dialog.)

As a side effect, several copies of the copyright notice and licence
text have moved from .rc files into C source. I've updated
CHECKLST.txt, but they won't stay there for long.