[IMP] - Make recurrence mechanism on contract line

Make recurrence mechanism on contract line and some other refactoring

[FIX] - Keep contract_cron on account_analytic_account model

contract_cron defined with no_update option.
Changing it, will cause issue to past version installation.

[IMP] - Fix recurring_next_date default value

recurring_next_date should have start_date as default value in prepaid policy
and start_date + invoicing_interval if postpaid

[FIX] - Fix test check no journal

[IMP] - Return created invoices on recurring_create_invoice

[IMP] - Specific process to compute recurring_next_date for  monthly-last-day

fixes: #198

[ADD] - Add Post-migration script to bring recurrence info from contract to contract lines

[ADD] - Add search filter based on date_end and recurring_next_date

 - not_finished filter in contract search view
 - finished filter in contract search view
 - Next Invoice group by in contract search view

[ADD] - Add unit tests

- cases to compute first recurring next date
- contract recurring_next_date
- contract date_end

[IMP] - Improve Unit tests

contract/migrations/12.0.2.0.0/post-migration.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 ACSONE SA/NV
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+
+def migrate(cr, version):
+    """Copy recurrence info from contract to contract lines."""
+
+    cr.execute(
+        """UPDATE account_analytic_invoice_line AS contract_line
+        SET recurring_rule_type=contract.recurring_rule_type,
+        recurring_invoicing_type=contract.recurring_invoicing_type,
+        recurring_interval=contract.recurring_interval,
+        recurring_next_date=contract.recurring_next_date,
+        date_start=contract.date_start,
+        date_end=contract.date_end
+        FROM account_analytic_account AS contract
+        WHERE contract.id=contract_line.contract_id"""
+    )