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)

This style logs everything through a single logging object and is
identical to using Python's `logging` module. The commonly-used
module-level logging functions are implemented as simple pass-thrus
to logging:

  import invokeai.backend.util.logging as ialog

  ialog.debug('this is a debugging message')
  ialog.info('this is a informational message')
  ialog.log(level=logging.CRITICAL, 'get out of dodge')
  ialog.disable(level=logging.INFO)
  ialog.basicConfig(filename='/var/log/invokeai.log')

Internally, the invokeai logging module creates a new default logger
named "invokeai" so that its logging does not interfere with other
module's use of the vanilla logging module. So `logging.error("foo")`
will go through the regular logging path and not add the additional
message decorations.

For more control, the logging module's object-oriented logging style
is also supported. The API is identical to the vanilla logging
usage. In fact, the only thing that has changed is that the
getLogger() method adds a custom formatter to the log messages.

 import logging
 from invokeai.backend.util.logging import InvokeAILogger

 logger = InvokeAILogger.getLogger(__name__)
 fh = logging.FileHandler('/var/invokeai.log')
 logger.addHandler(fh)
 logger.critical('this will be logged to both the console and the log file')

invokeai/backend/util/logging.py

@@ -28,22 +28,28 @@ 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)
+# module level functions
+def debug(msg, *args, **kwargs):
+    InvokeAILogger.getLogger().debug(msg, *args, **kwargs)
 
-def info(msg:str):
-    InvokeAILogger.getLogger().info(msg)
+def info(msg, *args, **kwargs):
+    InvokeAILogger.getLogger().info(msg, *args, **kwargs)
 
-def warning(msg:str):
-    InvokeAILogger.getLogger().warning(msg)
+def warning(msg, *args, **kwargs):
+    InvokeAILogger.getLogger().warning(msg, *args, **kwargs)
 
-def error(msg:str):
-    InvokeAILogger.getLogger().error(msg)
+def error(msg, *args, **kwargs):
+    InvokeAILogger.getLogger().error(msg, *args, **kwargs)
     
-def critical(msg:str):
-    InvokeAILogger.getLogger().critical(msg)
+def critical(msg, *args, **kwargs):
+    InvokeAILogger.getLogger().critical(msg, *args, **kwargs)
+
+def log(level, msg, *args, **kwargs):
+    InvokeAILogger.getLogger().log(level, msg, *args, **kwargs)
+
+def disable(level=logging.CRITICAL):
+    InvokeAILogger.getLogger().disable(level)
 
 class InvokeAILogFormatter(logging.Formatter):
     '''