Fix issues with applying wrong view-mode

- The view properties dialog mixed the details-view with
the compact-view (#285848).

- The view properties have been reset when applying a
setting from the "Dolphin Preferences" dialog. The rootcause
was that the obsolete DolphinSettings class implemented
the saving in a wrong way because of the recent refactoring
(will remove this class completely now to prevent such
issues in future).


FIXED-IN: 4.8.0