Sets on Applet::constraintsUpdated() the maximum content width for horizontal panels and the maximum content height for vertical panels as IconSize(KIconLoader::Panel) this makes vertical larger panels actually usable.

Some notes:
-it works only for applets that aren't forced to square
-in horizontal panels only for applets that don't have expandingDirections()=Qt::Horizontal
-in vertical panels only for applets that don't have expandingDirections()=Qt::Vertical

On other news the kickoff applets are modified to use this new feature

svn path=/trunk/KDE/kdebase/workspace/libs/plasma/; revision=770423