Provide before/after callbacks for project and mojo execution

As a build extension developer, I would like to be able to receive before/after callback events for project and mojo executions. For project-level events, I need MavenSession and ManveProject (obviously) as well as calculated project execution plain. For mojo executions I need MavenSession, ManveProject, MojoExecution and Mojo instances. The idea is to allow extensions observe and participate project build as a whole, not as set of independent mojo executions.