* Improved completion support for files with spaces

Filenames with spaces, both generally and for session names, will now
complete as expected.

* Misc shell script improvements

See discussion on:
1cca9e4b72

1. getplugs should work even if nnn is not run
2. Remove redundant ./ prefix
3. Update plugin docs

* getpulgs now asks before overwriting

* Forgot a space

xargs couldn't call function `dnd()` and I couldn't find a portable way
to do it, so I replaced it with a variable which I guess should work
fine.

For w/e reason the output from `which` causes problems with nnn
rendering. This commit silences the problematic lines.

* Implement plugins control of nnn + plugins

* Refactor plugins control code and fix getplugs to recognize hidden files

* Fix bug when going to dir on non-current context from plugin

* Fix some plugins to work on openbsd and freebsd

* Renamings

* Switch to -R flag in cp instead of -r; BSDs complain

* Change braces of function location

* Rewrite plugin creation in README and add new plugins to the table

* Update the fzcd script to include fzy or fzf

* Change plugin name resolve-link-dir -> lncd

* Fixing plugins README table

* Remove some cd plugins but add them as examples to plugins README

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