ERP5 Subcategory: Rename 'multiple_selection' subcategory to solve name conflicts.
Subcategory 'multiple_selection' has been renamed to 'multiple selection' to maintain consistency.
Earlier, whenever a new StandardCategory object was created with property_type 'multiple selection', one needed to change the elementary type explicilty to use it to generate property setters and getters.
The example for this can be seen from this commit: https://lab.nexedi.com/nexedi/erp5/commit/fd7387538a120307317c6c81cbe2399a866cdbb6 After this change, in the view, property type field couldn't recognize the property and displays (???multiple selection).
Also, everywhere in erp5, list_types do mention 'multiple selction' and not 'multiple_selection'. So, its better to maintain consistency in naming the subcategory.
The tests are running for this change via this test suite. (https://nexedi.erp5.net/test_suite_module/294) We wait for them to pass before merge, although I have rechecked the changes in a separate new instance.