critical path: Change relationship with graph builders

critical path: Change relationship with graph builders

This adds the critical path module as a child of the graph builder
module. It also creates the view output under the graph builder and
the view will open with the right execution graph selected.

Change-Id: Ibee665489f1e618dcf478e4ea092ae6c3f9d92e2
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/96666
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Hudson CI