Big update of packages to install

- remove not needed software from installation list (i.e., apt):
  + dropbox is entirely removed from the stack
  + same for most proprietory stuff (e.g., Microsoft)
- add a couple of packages (e.g., timeshift)
- update the pinned versions to up-to-date installs
- adjust hints/messages during installation
- minor adjustments (e.g., install only English, no more German support)