slapos_erp5: accounting period are only readable/writable by accountant

master/bt5/slapos_erp5/PortalTypeRolesTemplateItem/Accounting%20Period.xml

 <type_roles>
   <role id='Assignor'>
-   <property id='title'>Writable for Accountant</property>
+   <property id='title'>Accountant</property>
    <multi_property id='categories'>local_role_group/function</multi_property>
    <multi_property id='category'>function/accounting</multi_property>
    <multi_property id='base_category'>function</multi_property>