Core: Cosmetics

* Remove redundant namespace qualifiers
* Qt5-ify some signal/slot connections
* Replace some using Core::Internal with explicit namespace scopes

Change-Id: Id1aae05e2c6fc2992c2716e1f8f9e985c6e56122
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/coreplugin/actionmanager/actioncontainer.cpp

@@ -44,8 +44,8 @@
 
 Q_DECLARE_METATYPE(Core::Internal::MenuActionContainer*)
 
-using namespace Core;
-using namespace Core::Internal;
+namespace Core {
+namespace Internal {
 
 /*!
     \class ActionContainer
@@ -565,3 +565,5 @@ bool MenuBarActionContainer::canBeAddedToMenu() const
     return false;
 }
 
+} // namespace Internal
+} // namespace Core