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