showLoginBox: Improve initial focus
showLoginBox: Improve initial focus

- .focus on Chromium works only after a small delay for
  newly shown elements, it seems. At least some web search
  suggests that and focusing for the loginbox works only
  with the delay.

- I think, .one should be used instead of .on: The
  showLoginBox method can be called multiple times and the
  event only needs to be attached for that exact occassion.

- If the username is empty, it's probably nicer to focus it
  instead of the password.

jsxc/jsxc,jsxc/jsxc,jsxc/jsxc