[IMP+FIX] contract: Several things

- Add failing test for next invoice date before the last date invoiced
- raise an error when next invoice date before the last date invoiced
- Add note field to contract
- add new option: create_new_line_at_contract_line_renew
  Add a company config option to decide whether to create or to extend contract
  line at renew action
- extend contract line at renewal
- improve code: unify methods argument _renew_create_line and _renew_extend_line

contract/report/report_contract.xml

@@ -68,6 +68,11 @@
                                 </table>
                             </div>
                         </div>
+                        <div class="row" id="note">
+                            <strong>Notes: </strong>
+                            <br></br>
+                            <p t-field="o.note"/>
+                        </div>
                     </div>
                 </t>
             </t>