db_xml.py: put(): _setDefault(): Fixed bug where need to copy col_defaults before calling update() on it, to avoid modifying the input value (which may be reused by the caller, expecting it to be unmodified)

db_xml.py: put(): col_defaults param: Fixed bug where need to use None as default value, because col_defaults will be modified by put() and the {} default value is a global instance

mappings/VegCore-VegBIEN.csv: source table mappings: Set shortname to env var $source when it's not explicitly specified, because shortname is a required field of source

db_xml.py: put(): Pass through the values of nodes which are text nodes

db_xml.py: put(): put_(): Support setDefault() values which are text nodes, by passing text strings through when put() is run on all col_defaults entries

db_xml.py: put(): _setDefault(): Support setting multiple col_defaults at once by using the param names themselves as the column names

dicts.py: DictProxy: Implemented delitem()

bin/map: update_in_label(): Removed hardcoded source_id col_default, which is now set in mappings/VegCore-VegBIEN.csv's output root

mappings/VegCore-VegBIEN.csv: Set the source_id col_default to the datasource name using the new _setDefault() built-in function and _env()

db_xml.py: put(): Added _setDefault() built-in function, which adds an entry to col_defaults