DolphinSettingsDialog: Move focus to Okay button last

This commit changes the Tab order in Dolphin's Configure dialog so that the items which are visually at the end of the dialog are also last in the keyboard focus order when cycling through the interface using the Tab key.

Previously, the "Cancel", "Defaults", "Okay", and "Apply" buttons received focus prior to the actual contents of the pages which does not make sense from a workflow perspective.

This change should also make navigating this dialog easier when relying on screen readers because reading those buttons out prior to users even having a chance to change any setting did not make any sense.