Consistency in naming options in panel: hidden first (renamed from hidden last) and folders first

As said in the Nate's blog, It’s now possible to configure whether hidden files are shown before or after other files in Dolphin, and the default is “before”, as it used to be.

And there was a call to action: At least one of you will comment that those menu items don’t both say “first” or “last” 🙂 Good easy merge request opportunity… So I decided to make it.

The original functionality was introduced by !252 (merged)