For a better factoring and better management of all common features from...

For a better factoring and better management of all common features from digiKam KXmlGuiWindow based main windows
a new class named DXmlGuiWindow have been created. All digiKam main windows will be based on. Currently IE, BQM, and LT are done.
AlbumGUI and ImportUI still TODO.
This class replace FullScreenMngr as well. FullScreen mode are no managed through DXmlGuiWindow. Later more factoring will be done in this class, as
all Help digiKam dialogs (DB stats, Components info, etc...)
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