Followup to commit 54a36590 - start using the const overloads of the...

Followup to commit 54a36590 - start using the const overloads of the UMLObject::asUMLActor() to asUMLUseCase() functions.

Accessory changes:

umbrello/codegenerators/ada/adawriter.{h,cpp}
umbrello/codegenerators/pascal/pascalwriter.{h,cpp}
- At function isOOClass() declare UMLClassifier* argument `const'.

umbrello/uml1model/instanceattribute.{h,cpp}
- At function toString() add `const' qualifier.

umbrello/umlwidgets/entitywidget.cpp
- In functions calculateSize() and paint() rename local variable
  `casted' to `umlEA' (short for UMLEntityAttribute).

CCBUG: 442134