data: lambda handling

* implemented handling lambdas as functions
* functions can have child nodes now
* NameElements in NameHierarchy can have signatures now.
* fixed crash that occurred when message listener was used while being half way through its destruction process.

src/lib/data/name/NameHierarchy.cpp

@@ -23,7 +23,7 @@ void NameHierarchy::pop()
 	m_elements.pop_back();
 }
 
-std::shared_ptr<NameElement> NameHierarchy::back()
+std::shared_ptr<NameElement> NameHierarchy::back() const
 {
 	return m_elements.back();
 }