[IMP] product_contract: Add contract configurator instead of making tree not editable

Before this changes, when trying to edit a line of sale order, it was
opening the form of the line. But following the way to work of odoo
with sale event, we have make a new contract configurator that will
be opened when selecting a product of type contract.

product_contract/__init__.py

@@ -2,3 +2,4 @@
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
 from . import models
+from . import wizards