LibGUI: Start adding an automatic widget layout system.

My needs are really quite simple, so I'm just going to add what I need
as I go along. The first thing I needed was a simple box layout with
widgets being able to say whether they prefer fixed or fill for both
their vertical and horizontal sizes.

I also made a simple GStatusBar so FileManager can show how many bytes
worth of files are in the current directory.

SharedGraphics/Rect.h

@@ -52,6 +52,16 @@ public:
         return { x() + width() / 2, y() + height() / 2 };
     }
 
+    void set_location(const Point& location)
+    {
+        m_location = location;
+    }
+
+    void set_size(const Size& size)
+    {
+        m_size = size;
+    }
+
     void inflate(int w, int h)
     {
         set_x(x() - w / 2);