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/cpptoolsreuse.h

@@ -38,7 +38,7 @@ QT_FORWARD_DECLARE_CLASS(QStringRef)
 namespace CPlusPlus {
 class Symbol;
 class LookupContext;
-}
+} // namespace CPlusPlus
 
 namespace CppTools {