C++: Fix handling of Objective-C/C++

- Objective C/C++ was not enabled in highlighter.
- QMake project part for Objective C/C++ did not have ObjectiveC extension enabled.
- As languageFeatures.objCEnabled is a bitfield, it was actually always set to 0.
- Highlight ObjC class & protocol declarations.
- Highlight ObjC message passing.

Change-Id: I64d12c9509058d05f7adce94598cb7ce91727ac8
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/libs/cplusplus/MatchingText.cpp

@@ -203,6 +203,7 @@ static Tokens getTokens(const QTextCursor &cursor, int &prevState)
     features.cxx11Enabled = true;
     features.cxxEnabled = true;
     features.c99Enabled = true;
+    features.objCEnabled = true;
 
     SimpleLexer tokenize;
     tokenize.setLanguageFeatures(features);