CppTools: Use namespace CppTools consistently

There were quite a few classes using CPlusPlus namespace in the
CppTools plugin. Rename them and do some other small namespace
related coding style fixups.

Change-Id: I093fc1f3fc394fd9923e3f18d5f66522e288f21d
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/cpptools/doxygengenerator.h

@@ -37,9 +37,7 @@
 #include <QLatin1String>
 #include <QTextCursor>
 
-namespace CPlusPlus {
-class DeclarationAST;
-}
+namespace CPlusPlus { class DeclarationAST; }
 
 namespace CppTools {
 
@@ -97,6 +95,6 @@ private:
     QString m_commentOffset;
 };
 
-} // CppTools
+} // namespace CppTools
 
 #endif // DOXYGENGENERATOR_H