MEDIUM: applet: Set the appctx owner during allocation

MEDIUM: applet: Set the appctx owner during allocation

The appctx owner is now always a conn-stream. Thus, it can be set during the
appctx allocation. But, to do so, the conn-stream must be created first. It
is not a problem on the server side because the conn-stream is created with
the stream. On the client side, we must take care to create the conn-stream
first.

This change should ease other changes about the applets bootstrapping.