Girocco/Notify.pm: perform our own JSON body encoding

Girocco/Notify.pm: perform our own JSON body encoding

Instead of relying on the LWP::UserAgent to magically just
"do the right thing", go ahead and explicitly encode the
body of the JSON POST notification and pass that on to be
posted.

This was already being done for the 'application/json' type
and now we also do it for the 'application/x-www-form-urlencoded'
type as well.

This provides total byte-exact control over what actually
goes out over the wire for a JSON POST notification.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>