KDE dragon player collides with the name of the drag/drop dependency. On
archlinux the binary is renamed to `dragon-drag-and-drop`.

This change tries `dragon-drag-and-drop` before defaulting to `dragon`.

* Added 2 plugins for drag and drop support

These scripts uses https://github.com/mwh/dragon
and curl.

It allows nnn to drag and drop files either to other programs, or to
itself.

* added link to dependency and spelling

* added drag/drop-file scripts to readme table