Nicer /new URL for new accounts and redirect GET requests

If user types in https://nine.testrun.org/new manually
in the browser, at least Firefox and Brave suggest
to open the app after following the redirect.

cmdeploy/src/cmdeploy/genqr.py

@@ -6,7 +6,7 @@ import io
 
 
 def gen_qr_png_data(maildomain):
-    url = f"DCACCOUNT:https://{maildomain}/cgi-bin/newemail.py"
+    url = f"DCACCOUNT:https://{maildomain}/new"
     image = gen_qr(maildomain, url)
     temp = io.BytesIO()
     image.save(temp, format="png")