Drop deprecated code and revise log handling

[bl-young]

• old code for flowbysector.py is dropped
• deprecated functions are removed (primarily in validation.py, dataclean.py, fbs_allocation.py)
• data_source_script cleaning functions which now use more general approaches have been removed (e.g., BEA.py
• temp_data_source_functions.py have been moved to appropriate scripts
• logging functions are moved to flowsa_log.py (from settings.py) and duplicate code removed
  • log files are enabled for FBA and FBS (to be refined in future)