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.

Kernel/makeuserland.sh

@@ -10,6 +10,8 @@ make -C ../Terminal clean && \
 make -C ../Terminal && \
 make -C ../Clock clean && \
 make -C ../Clock && \
+make -C ../Launcher clean && \
+make -C ../Launcher && \
 make -C ../Userland clean && \
 make -C ../Userland && \
 sudo ./sync.sh