Used an exception so show error state.
Used a bool flag to make sure the error is only shown once PER error.
Updated tests to check for the correct Exception raised
Added Debug level logging for each deletion
Added error level logging when a delete has an exception
Built a test case for clean_output_directory in tests.utils.py
Updated `settings` in documentation to reflect new behavior
Removed the tip from the bottom of getting started since this setting should no longer break web servers pointing to the output directory.