Magnifying glass for Player and Output windows

Replace the 'inspector' menu in favor of a magnifying glass button at top right corner of imgui window for Player and Output preview. Disable the magnifying glass upon window unfocus.

src/UserInterfaceManager.h

@@ -305,6 +305,9 @@ class SourceController : public WorkspaceWindow
     float mediaplayer_timeline_zoom_;
     void RenderMediaPlayer(MediaSource *ms);
 
+    // magnifying glass
+    bool magnifying_glass;
+
     // dialog to select frame capture location
     DialogToolkit::OpenFolderDialog *captureFolderDialog;
     Screenshot capture;
@@ -339,6 +342,9 @@ class OutputPreview : public WorkspaceWindow
     // dialog to select record location
     DialogToolkit::OpenFolderDialog *recordFolderDialog;
 
+    // magnifying glass
+    bool magnifying_glass;
+
 public:
     OutputPreview();