Using type with potential namesakes should raise a warning

[dvojtise]

Similarly to #77
one can declare attribute, operation parameters using a type name that is ambiguous.
The following example is wrong because State currentState; has a namesakes (several eClasses named State in the environment) (and the reported error, isn't always straightforward, for example it only says that it cannot find the method step Couldn't find the 'step(EClassifier=State,EClassifier=EString)' service without indicating the qualified name)
(correct code is fsm::State currentState;)

This point is handled when opening a class (thanks to #77 ) but should also be reported in any other places we can use non fully qualified names (attribute definition, operation return type, arguments)