[ADD] product_contract: Create module

* Add contract functionality to `product.templates`
* Add logic to create contracts from `sale.order` that contains contract products.

product_contract/models/product_template.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 LasLabs Inc.
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from odoo import api, fields, models
+
+
+class ProductTemplate(models.Model):
+    _inherit = 'product.template'
+
+    is_contract = fields.Boolean('Is a contract')
+    contract_template_id = fields.Many2one(
+        comodel_name='account.analytic.contract',
+        string='Contract Template',
+    )
+
+    @api.onchange('is_contract')
+    def _change_is_contract(self):
+        """ Clear the relation to contract_template_id when downgrading
+        product from contract
+        """
+        if not self.is_contract:
+            self.contract_template_id = False