re #346: Import WIRIS plugin.

Doesn't actually build inside CKEditor. I can't help but wonder if
the WIRIS guys never actually tried building their plugin along with
all the other CKEditor plugins, because their directory structure is
subtly different from the other plugins in ways that breaks CKEditor's
build script.

Instead I've left it out of the CKEditor build plugins list, and it will
be placed into 'dist/assets/vendorPackages/ckeditor-yadayada/plugins/'
by a separate grunt target.

This is currently not usable without some manual configuration including:

- install 'php-fpm', 'php-mbstring'
- in your '/etc/nginx/conf.d/web-client-dev.conf' add a section something like:

    location ~ \.php$ {
      try_files $uri =404;
      include /etc/nginx/fastcgi_params;
      ifastcgi_param SCRIPT_FILENAME /shared/web-client/dist$fastcgi_script_name;
    }