This patch introduces a UI change: tabs only show an icon if it's not
the default one; that is to say, only if the user has actually customized
the icon. There are several reasons for this:
- Conceptual: When only non-default profile icons show up in the tab, it does a better job of highlighting the fact that a non-default profile is being used.
- Aesthetic: you no longer have the same icon in every tab by default, which looks bad and causes the eye to ignore it over time.
- Icon-specific: the utilities-terminal icon doesn't look good against a dark background (https://bugs.kde.org/show_bug.cgi?id=367696)
- Code hygiene: reduces a bit of redundancy in the session controller code.