KTitleWidget: move from QPixmap property to QIcon property
This adds two new properties "icon" and "iconSize" to the class and deprecates the "pixmap" property.
Some setter methods had already be changed to be about "icon", but getters & property have been still about a pixmap.
Also rendering the icon into a pixmap at the set call time loses all the advantages of having QIcon as a on-request pixmap factory, to render matching the current palette (think Breeze monochrome styled icons) or adapting to a changed style and its icon sizes.
Scratching my itch which I complained about here: https://phabricator.kde.org/D23927 :)
Patch for adaption of classes in KXmlGui: kxmlgui!7 (merged)
Edited by Friedrich W. H. Kossebau