erp5_pdm: use preferred category child item list method in my_variation_category_list field library.

Python script needs to be recompiled when they comes from a change of
class. This was done when business template was installing scripts, but
not when automatic migration from old catalog to new catalog was done.
So make sure to call _compile directly in changeObjectClass to make sure
Python Scripts would always work after a change of class.

Replace the airplane icon by a search button if not value is set on the field.
This make it more usable on mobile, where it's easier to browse than typing text.

Regression introduced by nexedi/erp5@cf1a0610

getSecurityQuery returns None when caller is superuser. Avoid passing it
to buildSQLQuery, as it would mistake security_query for a column name.