Rework verbosity

[guiguem]

Now that we have processors, we have to find a scheme for passing the logging verbosity from the main morpho executable down to all the processors (as is, it does not work...)

[laroque]

You want to set the level of the handler, not the logger. Setting the level of a specific logger is for overriding that: https://docs.python.org/2/howto/logging-cookbook.html#multiple-handlers-and-formatters