This reverts commit e226e8c889.

- distinct keybinds for single entry, range or all selection
- selecting a file/range/all files would turn selection mode on
- single file/range or all selection appends to selection
- any operation (cp, mv, rm, plugin/file execution, cmd prompt, launch app, spawn
  shell) on selection ends the selection mode
- selection buffer is cleared after mv, rm on selection
- repeat range selection on same file clears selection and exits seleciton mode
- basic check (won't work on dir reload) added to avoid duplicates in selection

The current file or dir name is exported in env var NN before running a cmd at
the command prompt or spawning a shell.

Export current file name as NCUR

This is a conveninece for nav-as-you-type mode.
With this program option, on pressing ^P, the filter is  executed as cmd.