Keep focus on jammr username textbox if empty

Set focus to the password textbox if the username is saved from a
previous run.  But if there is no username saved, don't move away the
focus.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Remove JammrServerBrowser JSON debug output

Don't log the server browser JSON response.  The qDebug() call was left
in during development.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>