ERP5 Property Sheets: Add property 'select_variable' to Standard Property object.
This change concerns with the addition of 'select_variable' property to 'Standard Property' object which is
required because while trying to display properties form for any ERP5 object which contains at-least one property
of selection or multiple selection type, rendering usually fails with an error "'select_varaible' is not
defined".
This is because of this section in properties.dtml file regarding rendering of properties of type selection
or multiple selection.
<dtml-elif "type=='selection'">
<dtml-if "hasProperty(select_variable)"><dtml-elif "type=='multiple selection'">
<dtml-if "hasProperty(select_variable)">This behaviour can be checked by trying to access properties form for any portal_type object.
Please review: @romain