[IMP] - improve cancel/uncancel process

[FIX] - Test if start_date is set before compute

[FIX] - date_end include in the period in auto_renew case

[FIX] - in suspension case, contract line should start a day after the end

[IMP] - confirm message on contract line cancel

contract/views/contract_line.xml

@@ -131,6 +131,7 @@
                 <button name="cancel" string="Cancel"
                         type="object"
                         icon="fa-ban text-danger"
+                        confirm="Are you sure you want to cancel this line"
                         attrs="{'invisible': [('is_cancel_allowed', '=', False)]}"/>
                 <button name="action_uncancel"
                         string="Un-cancel" type="object"