Start working on a simple Launcher app.

Let GButton have an optional icon (GraphicsBitmap) that gets rendered in the
middle of the button if present.

Also add GraphicsBitmap::load_from_file() which allows mmap'ed RGBA32 files.
I wrote a little program to take "raw" files from GIMP and swizzle them into
the correct byte order.

SharedGraphics/Size.h

@@ -13,6 +13,8 @@ public:
     int width() const { return m_width; }
     int height() const { return m_height; }
 
+    int area() const { return width() * height(); }
+
     void set_width(int w) { m_width = w; }
     void set_height(int h) { m_height = h; }