This also introduces a more global 'disabled' colour as defined by the style guide. I hope that we can gradually transition to this one, but we'll have to adjust some colours here and there.
Contributes to issue CURA-5876.
Conflicts:
plugins/PrepareStage/PrepareMenu.qml: Git was wrong, this was not really a conflict.
resources/qml/ActionButton.qml: With iconSource being modified on ui_rework_4_0 and me modifying the icon to be able to display it on the left hand side.
resources/qml/ActionPanel/OutputProcessWidget.qml: Git was wrong, not really a conflict.
resources/qml/ActionPanel/SliceProcessWidget.qml: Git was wrong, not really a conflict.
resources/qml/ExpandableComponent.qml: Both ui_rework_4_0 and me implemented a border around popups.
resources/qml/MainWindow/MainWindowHeader.qml: Git was wrong, not really a conflict.
resources/themes/cura-light/theme.json: Theme item was added in a place where I added whitespace.
Rather than the same as default_bold and default.
This also makes the extruder_icon font obsolete. Turns out it's actually just a very small font.
Contributes to issue CURA-5876.
