ui: Added shortcuts for navigating to next and previous reference in code view

* Added new class QtCodeNavigator between QtCodeView and QtCodeFileList that handles active ids and navigation
* Pass all files as initially collapsed to code view and decide in QtCodeNavigator which ones show content
* Rewrote requesting of active snippet display to top down approach
* Display other locations focused when active location changes
* Show corresponding edges when navigating references

src/lib_gui/qt/window/QtMainWindow.h

@@ -115,6 +115,8 @@ public slots:
 
 	void find();
 	void findFulltext();
+	void codeReferencePrevious();
+	void codeReferenceNext();
 	void overview();
 
 	void closeWindow();