This patch changes the mouseinterval to 0. And handles detection of
doubleclicking events internally.

This allows much faster response times for mouse clicks as nnn no longer
has to wait for ncurses to confirm what type of click it was.

It introduces a new config setting for changing how many milliseconds it
may take for a double click to be registered.

* unmount() ask for target if not found

unmount() now properly asks for which target to unmount if it cannot
automatically deduce which folder to unmount.

* no more automatic unmounts outside of cfgdir

* Implemented edit selection buffer

* Added checks and changed keybind

* Forgot check and style fixes

* Don't work late at night again

You forget things when you're tired

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