fixed display_class [2.11.3]

This version introduces multiple enhancements:

fixed problem with loading external templates for module templates
updated documentation

Details of additions/deletions below:
--------------------------------------------------------------

Modified:   /docs/template.md
            -- Updated --
                description about external templates

Modified:   /BLUE_FRAMEWORK/packages/CORE/display_class.php
            -- Updated --
                __construct, added parameter to _external method
                layout, added execute _external  method with module name as parameter
                _external, removed parameter default value, changed documentation