core: encode itemID base64
core: encode itemID base64

We need to encode the itemID base64 since it might contain slashes but the
context's HTTP server is created without SOUP_SERVER_RAW_PATHS enabled which
translates the URI encoded slashes to real slashes before handing the request
to us.

GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,Tarnyko/rygel,Tarnyko/rygel,GNOME/rygel,jku/rygel,Pelagicore/Media-Manager-Rygel-patched,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,luisbg/rygel,jku/rygel