Several warnings on Qt 5.12

[Aleix Pol]

Hi,
I've seen a bunch of warnings when running plasmashell under Qt 5.12.
I haven't had time to look into it but it looks legit. Possibly a
matter of using the right namespacing.

Cheers!
Aleix

Previously registered enum will be overwritten due to name clash:
PlasmaQuick::Dialog.FullScreen
Possible conflicting items:
    Plasma::Types.Location.FullScreen from scope Plasma::Types
injected by PlasmaQuick::Dialog->Plasma::Types
    PlasmaQuick::Dialog.Visibility.FullScreen from scope QWindow
injected by PlasmaQuick::Dialog
Previously registered enum will be overwritten due to name clash:
PlasmaQuick::Dialog.NoBackground
Possible conflicting items:
    Plasma::Types.BackgroundHints.NoBackground from scope
Plasma::Types injected by PlasmaQuick::Dialog->Plasma::Types
    PlasmaQuick::Dialog.BackgroundHints.NoBackground from scope
PlasmaQuick::Dialog injected by PlasmaQuick::Dialog
Previously registered enum will be overwritten due to name clash:
PlasmaQuick::Dialog.StandardBackground
Possible conflicting items:
    Plasma::Types.BackgroundHints.StandardBackground from scope
Plasma::Types injected by PlasmaQuick::Dialog->Plasma::Types
    PlasmaQuick::Dialog.BackgroundHints.StandardBackground from scope
PlasmaQuick::Dialog injected by PlasmaQuick::Dialog
Previously registered enum will be overwritten due to name clash:
DesktopView.FullScreen
Possible conflicting items:
    DesktopView.Visibility.FullScreen from scope QWindow injected by DesktopView
    DesktopView.WindowType.FullScreen from scope DesktopView injected
by DesktopView
Previously registered enum will be overwritten due to name clash:
QQuickGridView.Center
Possible conflicting items:
    QQuickGridView.TransformOrigin.Center from scope QQuickItem
injected by QQuickGridView
    QQuickGridView.PositionMode.Center from scope QQuickItemView
injected by QQuickGridView
Previously registered enum will be overwritten due to name clash:
QQuickGridView.Center
Possible conflicting items:
    QQuickGridView.TransformOrigin.Center from scope QQuickItem
injected by QQuickGridView
    QQuickGridView.PositionMode.Center from scope QQuickItemView
injected by QQuickGridView