Polish IPv4 settings dialog
Summary:
Set the hostname as the placeholder text, which will be used if the hostname is empty.
Show an specialValueText and a suffix on the timeout field.
Make sure we don't try to save the dialog if the parent window has been deleted.
Test Plan: Used it
Reviewers: Plasma, jgrulich
Reviewed By: jgrulich
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22394