General update to logging.

Make all loggers inherit from pyclaw logger.
Add convenience function for setting console logging level in controller (h/t @ahmadia).

I see two main use cases where one wants to adjust the logging:

1. Turn off logging to stdout (IPython notebooks)
2. Turn off all logging (or set all to CRITICAL) (Shaheen)

For 1, we want to selectively modify the level of the console handler for the controller logger.  This can now be done via

    claw.verbosity = 0

Meanwhile, the controller will still write to the log file.

For case 2, one can do 

    import logging
    logger = logging.getLogger()
    logger.setLevel(logging.CRITICAL)

which propagates to the other loggers.


For completeness, the logger name changes are:

io -> pyclaw.io
solution -> pyclaw.solution
evolve -> pyclaw.solver

and there is a new logger `pyclaw.controller`.