Preliminary work for full UST support

Add hashtable support for all UST data structure. At this point, enable
channel and event works with the global UST domain. The interaction with
the ust consumer has problems for now thus not working at this stage.

NOTICE: This commit does NOT work with the user space tracer yet. Please
refer to next commit for working version.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>