Analysis: Add the dependency graph plugin and base classes

Adds a new plugin: org.eclipse.tracecompass.analysis.graph.core and the base
classes used to represent a dependency graph.

Change-Id: I8bd45263cbf02b42d62b44868409b50ac46125ac
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>
Reviewed-on: https://git.eclipse.org/r/41477
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>