DolphinPart: provide a way to switch between view modes in konqueror.

DolphinPart: provide a way to switch between view modes in konqueror.
Factorized those actions between dolphinmainwindow and dolphinpart (see new methods in dolphinview), and simplified mainwindow code by using the signal from the action group and the QVariant data of the actions (standard Qt4 solution for a group of actions).

svn path=/trunk/KDE/kdebase/apps/; revision=723871