Actual parameters not updated when structural feature's name changes

[Matthias Schoettle]

When the name of existing structural features changes, that are passed as parameters in messages, the parameter description is not updated.

For example:

boolean test := false; (declaration of a new property using an assignment statement)
doSomething(test); (message call onto some object)

If test is renamed, the name in the message call is not updated.

[Matthias Schoettle]

Resolves #268: Changes the item provider of StructuralFeatureValue and ParameterValue to be stateful and introduces a ChangeListener that can react on changes regarding referenced element's properties (e.g., value and parameter respectively). A stateful item provider is required, because the change listener makes use of getTarget(), which won't work if there are multiple different instances of one of the two.

→ <<cset 3556b378b600>>