In Qt5 the palette was introduced in the Control object (part of Qt-
Quick-Controls-2).
In Qt6 this property was moved to the superclass 'Item'.
This means that we no longer need to refer to a control when using a
palette, every single thing in QtQuick is an Item, afterall.
This gives the dark-theme a make-over with better colors, more colors
coming from the palette and this makes the conceptual usage between the
mobile and desktop clients of colors to be in-line.
The 'text' and 'windowText' were both used like they were the same
thing, which they currently are but don't have to be.
Now migrate the various cases where to we use 'text' to 'windowText'.
This choice is made because the Label object uses windowText by default.
In future we might want to make the 'text' one have a slightly different
color. Its still used in Qt components like the popup menu.
tomFlowee