[REM] models: remove the magic methods signal_XXX()

addons/account/account_invoice.py

addons/mrp/mrp.py

addons/mrp/procurement.py

addons/mrp/stock.py

addons/point_of_sale/point_of_sale.py

addons/purchase/purchase.py

addons/purchase_requisition/purchase_requisition.py

addons/sale/wizard/sale_make_invoice.py

addons/sale_stock/sale_stock.py

addons/sale_stock/test/cancel_order_sale_stock.yml

addons/sale_stock/test/picking_order_policy.yml

addons/stock/wizard/make_procurement_product.py

addons/website_quote/controllers/main.py

openerp/addons/base/ir/ir_actions.py

openerp/models.py