Details view: Optionally remember user changed column-widths

Details view: Optionally remember user changed column-widths

If the user changed a column-width in the details-view, up to now
the width got reset when changing a directory or when restarting
Dolphin. Now the column-widths automatically get remembered for each
directory in case if the user has modified the width. The automatic
resizing is still turn on per default. The storing of the custom
column-width can easily be reset by right clicking on the header and
selecting "Automatic Column Widths" from the context-menu.

Some finetuning is still necessary (e.g. the "Adjust View Properties"
dialog currently is not aware about this setting) but this will
be fixed during the next weeks.

BUG: 264434
FIXED-IN: 4.9.0