server: Add "Sever:" header

We append a Server header to the HTTP response.

Default is plugin/version g_get_prgname()/version DLNA/1.51 UPnP/1.0

It is configurable on a per-plugin base using the key "server-name"

Signed-off-by: Jens Georg <mail@jensge.org>

https://bugzilla.gnome.org/show_bug.cgi?id=747816