MEDIUM: stream: make stream_new() always set the target and analysers

MEDIUM: stream: make stream_new() always set the target and analysers

It doesn't make sense that stream_new() doesn't sets the target nor
analysers and that the caller has to do it even if it doesn't know
about streams (eg: in session_accept_fd()). This causes trouble for
H2 where the applet handling the protocol cannot properly change
these information during its init phase.

Let's ensure it's always set and that the callers don't set it anymore.

Note: peers and lua don't use analysers and that's properly handled.