Fix: big relayd cleanup and refactor

Fix: big relayd cleanup and refactor

Due to a number of race conditions between the live feature and the data
threads, we had to refactor the relayd which mostly splits the different
objects in their own files creating APIs for each of them.

That done, we are able to remove duplicate code, centralize code path
to help with cleanup and having a flow that makes more sense when
handling multiple objects.

This commits adds a lot of fixes with the live feature and cleanup code
path of a session since some objects are shared between threads like
ctf-trace and stream.

So yeah, this is quite a BIG commit and unfortunately this work was
essential in order to fix a lof of issues and have a way more
maintainable code base for the relayd.

Signed-off-by: Julien Desfossez <julien.desfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Conflicts:
	src/bin/lttng-relayd/lttng-relayd.h