put singletons into their namespace

src/singletons/helper/completionmodel.hpp

@@ -7,6 +7,7 @@
 #include <string>
 
 namespace chatterino {
+namespace singletons {
 class CompletionModel : public QAbstractListModel
 {
 public:
@@ -39,3 +40,4 @@ private:
     QString channelName;
 };
 }
+}