Update wording: KDE usage, obsolete technologies

- preload is about Plasma or at least the desktop (needs to check
  whether the special key works for Plasma only);
- cleanup in the about page:
  * remove a bit of obsolete plugin types, and name them by
    technology (NPAPI) instead by the original company;
  * more highlight on OpenJDK as primary Java SE implementation;
  * few links updated.