New port: x11/j4-dmenu-dekstop: Fast desktop menu (i3-dmenu-desktop replacement)

j4-dmenu-desktop is a replacement for i3-dmenu-desktop. It's purpose is to
find .desktop files and offer you a menu to start an application using
dmenu. Since r2.7 j4-dmenu-desktop doesn't require i3wm anymore and should
work just fine on about any desktop environment.

You can also execute shell commands using it.

WWW: https://github.com/enkore/j4-dmenu-desktop

Reviewed by: mat
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D18911