KDM14 — Confusion in the type of the method getCodeElement in ClassUnit

The type is CodeItems. So we have a method getCodeElements that in fact returns a list of CodeItems.

This leads to code written like this :
List<CodeElement> myList= cu.getCodeElements();
Which causes class cast exceptions since a CodeItem isn't a CodeElement

The method should be renamed getCodeItems, or type made more generic to AbstractCodeElement

Change the type of property codeElements in ClassUnit and TemplateUnit to AbstractCodeElement

Currently the type is CodeItems; it should be made more generic to AbstractCodeElement in order to avoid confusion with the type of hte generated method getCodeElement and to allow extensions.