Change the way ext_colorlog.py locates its config
Change the way ext_colorlog.py locates its config

By having the Meta.label be dynamically fetched when "colorize" is set, one can subclass ColorLogHandler to add further functionality (ie. mailing when a fatal error occurs). 
Now a subclass Handler can be defined, its own class Meta sets the config_defaults and the original ColorLogHandler receives the config from it.
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