Remove overlay residues when navigating to subdirs/parent dirs
New feature: Open all files and/or dirs in the current region

This requires a currently active region and does not try to
compensate for user stupidity (overly large region etc.).
New feature: file/dir marking and opening of all marked files/dirs

The workflow is like this:
  1. Manually mark files and/or directories.
  2. Open all marked files and/or directories (The files/dirs are
     then automatically unmarked for convenience).