* make Makefile more packaging friendly

* packagecore: run `strip` before installing

The replacement keys are:

^J - toggle du mode
^Y - quit

The change is done because ^S, ^Q keybinds are lost in the following case:
- start nnn
- navigate to a different directory
- spawn a shell
- exit the shell

The issue happens only with the 'special' keybinds like ^S, ^Q, ^Z... which get
their original shell interpretation back.

So we are replacing these 2 keybinds with 2 'non-special' combinations.

New keys:

- bookmark prompt (^B)
- pin directory (B)

The intention of the change is to facilitate opening the bookmark prompt in
navigate-as-you-type mode. The bookmark prompt is used more than the pin
current directory option.

Enabled functionality:

- Copy file path (^K)
- Run desktop search utility (^/)
- Rename file (^R)
- Open with... (^O)
- Pin current directory (^B)
- Visit pinned directory (^V)
- Extract archive (^X)

- For standard view, use ISO 8601 date format.
- For detailed view (i.e. stat), use default Linux date
  format. Also, remove GMT offset to avoid confusion in
  determining source of offset when reading alongside
  the local time zone.

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