logic: improved indexer coverage for using decls, using directives

* moved source code for solving names of NestedNameSpecifiers to new CxxSpecifierNameResolver.
* implemented recording of UsingDirectives.
* implemented using file as context for using directives and using directive decls if no other context is available.
* re-implemented recording of the auto keyword

src/lib/data/name/NameElement.cpp

@@ -19,6 +19,8 @@ NameElement::Signature NameElement::Signature::deserialize(const std::string& se
 }
 
 NameElement::Signature::Signature()
+	: m_prefix("")
+	, m_postfix("")
 {
 }