Fix inspector window sometimes not hiding

When the f shortcut is quickly pressed, the inspector window will
sometimes open and remain open even though it should automatically
close. This commit ensures the window closes by capturing the f key
release event from the main window in addition to the inspector window.

rtgui/rtwindow.h

@@ -85,6 +85,7 @@ public:
     void addBatchQueueJobs      (const std::vector<BatchQueueEntry*>& entries);
 
     bool keyPressed (GdkEventKey* event);
+    bool keyReleased(GdkEventKey *event);
     bool on_configure_event (GdkEventConfigure* event) override;
     bool on_delete_event (GdkEventAny* event) override;
     bool on_window_state_event (GdkEventWindowState* event) override;