Allow plotting of all examples from memory in PyClaw

This PR makes use of code introduced in https://github.com/clawpack/pyclaw/pull/344 to enable plotting of all PyClaw examples interactively from memory, via

    import clawpack.pyclaw.examples as ex
    claw = ex.woodward_colella_blast.setup()
    claw.run()
    claw.plot()