Fixes #656

* added support webp format

* update nuke plugin with support webp format

Selection is cleared after successful:
- file removal
- batch rename
- link creation

However, selection is not cleared after:
- archive creation: user may want to delete the files after archiving

Both Pistol and `scope.sh` are run `file --mimetype` or an equivalent, internally.
Thus, for speed, it's better to run them before almost anything else.

* Easier to browse plugin README.md

* Splits are inverted

* trying to fix kitty splits

* Correctly restores the kitty layout

* More clear comments

* Easier to browse plugin README.md

* Splits are inverted

* $SPLIT clarification and default values for $SPLIT and $TERMINAL

* Unified preview-tui and preview-kitty

* Remove preview-kitty

* No need to set $TERMINAL

* fix undeclared variable

* Integrated support for scope.sh

* Review fixes

* allow_remote_control must be enabled on kitty

* Documentation, kitty splits and images fallback

* fix restoring kitty layout

In the dash shell, when `exec < fifo` is interrupted by SIGCHLD, it exits.
So we replace it with `cat fifo |`.

Issue discussed in #614

Fixed typo in preview-kitty.

Thanks @Kabouik!

* Added GPG encrypt and decrypt plugins

* Made description more descriptive

Co-authored-by: Todd Yamakawa <todd.yamakawa@arm.com>