add logging support

This commit adds invokeai.backend.util.logging, which provides support
for formatted console and logfile messages that follow the status
reporting conventions of earlier InvokeAI versions.

Examples:

   ### A critical error     (logging.CRITICAL)
   *** A non-fatal error    (logging.ERROR)
   ** A warning             (logging.WARNING)
   >> Informational message (logging.INFO)
      | Debugging message   (logging.DEBUG)

invokeai/backend/util/logging.py

@@ -0,0 +1,107 @@
+"""invokeai.util.logging
+Copyright 2023 The InvokeAI Development Team
+
+Logging class for InvokeAI that produces console messages that follow
+the conventions established in InvokeAI 1.X through 2.X.
+
+
+One way to use it:
+
+from invokeai.backend.util.logging import InvokeAILogger
+
+logger = InvokeAILogger.getLogger(__name__)
+logger.critical('this is critical')
+logger.error('this is an error')
+logger.warning('this is a warning')
+logger.info('this is info')
+logger.debug('this is debugging')
+
+Console messages:
+     ### this is critical
+     *** this is an error ***
+     ** this is a warning
+     >> this is info
+        | this is debugging
+
+Another way:
+import invokeai.backend.util.logging as ialog
+ialog.debug('this is a debugging message')
+"""
+import logging
+import sys
+
+def debug(msg:str):
+    InvokeAILogger.getLogger().debug(msg)
+
+def info(msg:str):
+    InvokeAILogger.getLogger().info(msg)
+
+def warning(msg:str):
+    InvokeAILogger.getLogger().warning(msg)
+
+def error(msg:str):
+    InvokeAILogger.getLogger().error(msg)
+    
+def critical(msg:str):
+    InvokeAILogger.getLogger().critical(msg)
+
+class InvokeAILogFormatter(logging.Formatter):
+    '''
+    Repurposed from:
+    https://stackoverflow.com/questions/14844970/modifying-logging-message-format-based-on-message-logging-level-in-python3
+    '''
+    crit_fmt = "### %(msg)s"
+    err_fmt = "!!! %(msg)s !!!"
+    warn_fmt = "** %(msg)s"
+    info_fmt = ">> %(msg)s"
+    dbg_fmt = "   | %(msg)s"
+
+    def __init__(self):
+        super().__init__(fmt="%(levelno)d: %(msg)s", datefmt=None, style='%')
+
+    def format(self, record):
+        # Remember the format used when the logging module
+        # was installed (in the event that this formatter is
+        # used with the vanilla logging module.
+        format_orig = self._style._fmt
+        if record.levelno == logging.DEBUG:
+            self._style._fmt = InvokeAILogFormatter.dbg_fmt
+        if record.levelno == logging.INFO:
+            self._style._fmt = InvokeAILogFormatter.info_fmt
+        if record.levelno == logging.WARNING:
+            self._style._fmt = InvokeAILogFormatter.warn_fmt
+        if record.levelno == logging.ERROR:
+            self._style._fmt = InvokeAILogFormatter.err_fmt
+        if record.levelno == logging.CRITICAL:
+            self._style._fmt = InvokeAILogFormatter.crit_fmt
+
+        # parent class does the work
+        result = super().format(record)
+        self._style._fmt = format_orig
+        return result
+
+class InvokeAILogger(object):
+    loggers = dict()
+    
+    @classmethod
+    def getLogger(self, name:str='invokeai')->logging.Logger:
+        if name not in self.loggers:
+            logger = logging.getLogger(name)
+            logger.setLevel(logging.DEBUG)
+            ch = logging.StreamHandler()
+            fmt = InvokeAILogFormatter()
+            ch.setFormatter(fmt)
+            logger.addHandler(ch)
+            self.loggers[name] = logger
+        return self.loggers[name]
+
+def test():
+    logger = InvokeAILogger.getLogger('foobar')
+    logger.info('InvokeAI initialized')
+    logger.info('Running on GPU 14')
+    logger.info('Loading model foobar')
+    logger.debug('scanning for malware')
+    logger.debug('combobulating')
+    logger.warning('Oops. This model is strange.')
+    logger.error('Bailing out. sorry.')
+    logging.info('what happens when I log with logging?')