class_find_child_property
Description:
public static unowned ParamSpec class_find_child_property (ObjectClass mclass, string property_name)
  
  This function is only intended to be used when implementing new canvas item models, specifically layout container item models such as CanvasTableModel.
It finds a child property of a canvas item class by name.
Parameters:
| mclass | |
| property_name | the name of the child property to find | 
Returns:
| The ParamSpec of the child  property or null
             if  |