[FIX] ir_fields: add missing class ImportWarning (was removed from orm.py by accident)
[IMP] fields: reimplement property fields to improve performance, and add search
[IMP] fields: add new-style property (company-dependent) fields
[IMP] models: be more tolerant with unknown fields in method onchange
[FIX] fields: missing conversion column -> field
[FIX] fields: typing error in property.to_field_args()
[FIX] ir_property: fix implementation of property field search

To search a property field of type 'many2one':
 - first retrieve records from the comodel that match the condition,
 - then search properties with value_reference in the refs of the records,
 - finally retrieve the model records that correspond to matching properties.

The fixes:
 - retrieve records in the comodel with name_search() instead of search()
 - generate refs for the records with the comodel instead of the model
[IMP] fields: add missing description of company-dependent fields
[IMP] fields: add documentation
merge upstream