Instead of using 'pi' as default, try to get the username of
the current user from the OS.
May not always work. (e.g. some Windows users may not have
setup a username themselves, but may be using a default user
created by the PC vendor).
Closes#497
In the "advanced settings" dialog, if "X" instead of
"apply settings" is clicked, it is seen as "cancel" and
no settings are applied.
If there do are saved settings, make sure to ask the
user on pressing "write" if they do want the saved settings
applied, instead of applying no settings.
Implemented as "validator" which will cause that if an user
presses a key that is not allowed, it will not register.
Saves having to add an error message that would need to be
translated to different languages.
Closes#474
