Implement basic design of Landing page in QML

Basic design in defined in https://bugreports.qt.io/browse/QDS-6563

We need to integrate with the theming engine. Unfortunately, the theming engine is in the QmlDesigner plugin, which is enabled. Linking against the QmlDesigner plugin is not advised.

Utils::Theme is available and can be used. Only a handful of colors should be required. We can expose those as properties of the backend. Henning can be asked for details.

The font TitilliumWeb can be used like this:

 readonly property alias titilliumWeb_regular: fontLoader_regular.name
	
    property FontLoader fontLoader_light: FontLoader {
        id: fontLoader_light
        source: ""qrc:/studiofonts//TitilliumWeb-Light.ttf"
    }

The qrc file will is loaded by the welcome page of Qt Creator. This should be sufficient.