Refactored logging into its own class. No more global variables for
logging. No need to use logger_debug() (with an underscore) any more -
now we can use logger.debug() (with a dot) instead, which calls the
debug method of our custom Logger class.  The "logger" object used
throughout the Launcher code is now a singleton object of our custom
Logger class, defined within the logger/Logger.py module.  The singleton
logger object can be imported with "from logger.Logger import logger".
This refactoring fixes issue CVLFAB-654 ("logging in LoginTask does not
appear in log").