rygel: Update to 0.28.2

Update to latest version. This mainly fixes file uploading,
which did not work in previous version (see upstream commit
"1d45866a3fd7ca47bdbea60156bd18b994710662" among others).

sqlite3 is now required to build whole rygel, as some
media-export plugin routines have been centralized ;
libunistring also improves collation logic if present.

Rygel will not keep running anymore when its "plugins"
folder is absent or empty. Thus, to avoid disappointments,
we now RRECOMMEND at least the media-export plugin.

Signed-off-by: Manuel Bachmann <mbc@iot.bzh>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>