Merged "Methods" and QML "Functions" locator filters

They're still separate filters, but by default they share the same
prefix, which will now make sure that only one entry shows up in the
list of filters.

Done-with: Christian Kamm
Task-number: QTCREATORBUG-4796

src/plugins/cpptools/cppfunctionsfilter.h

@@ -46,7 +46,7 @@ public:
     CppFunctionsFilter(CppModelManager *manager);
     ~CppFunctionsFilter();
 
-    QString displayName() const { return tr("Methods"); }
+    QString displayName() const { return tr("Methods and functions"); }
     QString id() const { return QLatin1String("Methods"); }
     Priority priority() const { return Medium; }
 };