ui: load project via MenuBar

This change adds a MenuBar to QtMainWindow and adds an action for opening a different project settings XML file. The
message MessageLoadProject is thereon used to load a new project in the Application and clearing the Storage.

src/lib/data/location/TokenLocationCollection.h

@@ -43,6 +43,8 @@ public:
 
 	TokenLocation* addTokenLocationAsPlainCopy(const TokenLocation* location);
 
+	void clear();
+
 private:
 	TokenLocationFile* createTokenLocationFile(const std::string& filePath);