Send filter expression string to session daemon

Send the filter expression string along with the filter's bytecode
to the session daemon. The session daemon now stores the filter
expression. This makes it possible to list the filter's expression
when listing events.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Save UST domain
bugfixes
JUL domain support
XSD update to store session outputs
Session output save support
Error handling overhaul