Add 'publication_date' to exceptions list and modify/create function to handle in extract_base_layer.py

[tyt3]

For 'publication_date' under MONOGRAPH_ITEM_MODS_MAP, 'originInfo > dateIssued' cannot have any attributes.

In data_layer_config.py:
'publication_date': {'bs_exp':['originInfo > dateIssued',]},