Comes with a unit test
Also ran the following in qml scene and changed settings, the icon item would adjust itself:
```
import QtQuick 2.2
import org.kde.plasma.core 2.0 as PlasmaCore
Item {
width: 500
height: 500
PlasmaCore.IconItem {
source: "user-home"
}
}
```
I wonder if we shouldn't scale the implicit size with Units